JP5108628B2 - Method for forming highly adhesive metal nanoparticle sintered film - Google Patents

Description

  The present invention relates to a method for forming a metal nanoparticle sintered body film exhibiting high adhesion to a copper layer as an underlayer. In particular, when a polyimide coat film that covers the copper layer surface of the underlayer is provided and the metal nanoparticle sintered body film is selectively formed in the opening formed in the polyimide coat film, the copper layer of the underlayer is formed. On the other hand, it is related with the method of forming the metal nanoparticle sintered compact film | membrane which shows high adhesiveness. For example, for a copper layer as an underlayer that can be applied to the production of a fine wiring substrate (Interposer) for SIP (System in Package) or a fine wiring substrate (Substrate) for SIB (System in Board) The present invention relates to a method of forming a metal nanoparticle sintered body film exhibiting high adhesion.

  In the multilayer wiring board, an insulating layer is provided between the lower wiring layer and the upper wiring layer. For conduction between the upper and lower wiring layers, a hole passing through the insulating layer separating the two layers is formed, and interlayer conduction through via holes is used.

  In the manufacturing process of a multilayer wiring board, for example, a build-up board, an insulating layer is formed so as to cover the lower wiring layer. A through-hole portion used for interlayer conduction through a via hole is provided so as to penetrate the insulating layer and expose the surface of the lower wiring layer in the opening. When the upper wiring layer is formed on the upper surface of the insulating layer, a conductive layer is formed so as to fill the through-hole portion and cover the surface of the lower wiring layer exposed to the opening, thereby achieving interlayer conduction through the via hole. Yes.

  When an upper wiring layer is formed using an electroless plated copper layer, the electroless plated copper layer is also used for a conductor layer for interlayer conduction through a via hole. Specifically, the conductor layer for interlayer conduction through the via hole and the upper wiring layer electrically connected to the conductor layer are integrally formed.

  A multilayer wiring board has also been proposed in which an upper wiring layer is formed using a conductive layer formed using a conductive metal paste instead of an electroless plating metal layer. For example, as a conductive medium, using metal nanoparticles having an average particle diameter of 1 to 100 nm and using a conductive metal paste to which an organic binder resin used for resin adhesion to the insulating layer surface is added, the upper layer A method of manufacturing a multilayer wiring board in which a wiring layer is formed has been proposed (see Patent Document 1). At that time, the coating film layer of the conductive metal paste is drawn in a predetermined pattern shape so as to cover the upper surface of the insulating layer, the side wall surface of the through hole, and the surface of the lower wiring layer exposed in the opening. The coating film layer of this conductive metal paste is subjected to a heat treatment at a temperature of 250 ° C. or lower to produce a sintered body layer in which metal nanoparticles having an average particle diameter of 1 to 100 nm are sintered at a low temperature. This metal nanoparticle sintered body layer is bonded and fixed to the upper surface of the insulating layer and the side wall surface of the through hole using the added organic binder resin. The surface of the lower wiring layer exposed to the opening of the through hole is in close contact with the metal nanoparticle sintered body layer, and interlayer conduction through the via hole is achieved. In this method, in the conductive metal paste used, a coating layer made of an organic compound capable of coordinating with a metal element contained in the metal nanoparticle is provided on the surface of the metal nanoparticle, and the coating layer is formed. The metal nanoparticles are stably dispersed in the solvent while being held. Furthermore, in the conductive metal paste, a trapping substance capable of acting on the organic compound that constitutes the coating layer is blended when heated.

  In addition, in the production process of a multilayer wiring board, for example, a build-up board, both the lower wiring layer and the upper wiring layer use a conductive paste, and an insulating resin layer for interlayer separation is used as an insulating paste. There has also been proposed a method of making a batch by using (see Patent Document 2). In this manufacturing process, a conductive paste coating film layer for a lower layer wiring is formed on an insulating substrate by using an inkjet method for drawing, and conduction between upper and lower layers is performed with respect to a laminated portion where an upper layer wiring layer pattern overlaps. An insulating paste coating film layer is formed for interlayer separation only in a partial region covering the other part except for the laminated part to be planned. Further, a conductive paste coating film layer for upper layer wiring is laminated and heat-treated to produce a conductor layer from each conductive paste coating film layer and an insulator layer from the insulating paste coating film layer. As a result, a multilayer wiring layer is formed in which the layers are separated from each other by the insulating film in the partial region, and the upper and lower wiring layers are connected and conductive at the laminated portion where the formation of the insulating film is omitted. That is, at the portion where the conductive paste coating film layer for the lower wiring and the conductive paste coating film layer for the upper wiring are laminated, the heat treatment is performed with the conductive paste coating film layers of both layers in direct contact with each other. As a result, an integrated conductor layer is formed in the laminated portion. In the partial region where the insulating paste coating film layer is in contact with the conductive paste coating film layer for the lower layer wiring, heat treatment is simultaneously performed. Therefore, the insulating resin is applied to the upper surface of the lower wiring layer and the lower surface of the upper wiring layer. The layer is in a closely bonded state.

  In addition, a method of forming a plating substitute conductive metal film using a metal nanoparticle dispersion has been proposed (see Patent Document 3). By applying a metal nanoparticle dispersion liquid that does not contain an organic solder component to the surface of the plating underlayer on which an electroless plating layer can be formed, applying heat treatment, and performing low-temperature sintering of the metal nanoparticles The metal nanoparticle sintered body layer is formed on the surface of the plating base layer. At that time, the adhesion between the surface of the plating underlayer and the metal nanoparticle sintered body layer is achieved by forming an intermetallic bond between the metal nucleus (plating nucleus) on the surface of the plating underlayer and the metal nanoparticle. . Therefore, it has been proposed to use the plating substitute conductive metal film formed by applying the above method for the purpose of substituting the portion for forming the electroless plating layer on the surface of the plating base layer when the wiring board is manufactured. . For example, use as a substitute layer for a plated film for through-holes formed on the inner wall surface of a through-hole penetrating a double-sided wiring board has been proposed.

  An interposer having a structure in which high-density fine wiring is stacked in multiple layers is being used as a fine wiring substrate for SIP (System in Package) in which a plurality of LSIs are stacked and connected in multiple layers. At that time, a polyimide layer is used as an interlayer insulating layer provided between the multilayer wiring layers constituting the interposer. Specifically, a photosensitive polyimide is adopted, a lithography method is applied, and the photosensitive polyimide is exposed to light and developed to form a via hole in the interlayer insulating layer. Interlayer conduction through the via hole is achieved by embedding a metal layer in the manufactured via hole. In particular, the use of a chemically amplified positive photosensitive polyimide as the photosensitive polyimide and solubilizing the light-exposed portion is being promoted.

  In addition, when preparing a sintered layer of metal nanoparticles as an upper wiring layer on the upper surface of the polyimide layer of the interlayer insulating layer, in order to avoid wetting and spreading of the conventionally applied metal nanoparticle dispersion, A liquid repellent coating layer is formed on the upper surface of the polyimide layer except for the coating area. Similarly, when producing a sintered body layer of metal nanoparticles in a predetermined region on the surface of the metal layer, conventionally, in order to avoid wetting and spreading of the applied metal nanoparticle dispersion, A liquid repellent coating layer is formed on the upper surface of the layer. That is, since the dispersion liquid constituting the metal nanoparticle dispersion liquid has poor wettability with respect to the surface of the liquid repellent coating layer, the phenomenon that the metal nanoparticle dispersion liquid wets and spreads around the coating region is avoided.

  Actually, once the liquid repellent coat layer is formed so as to cover the entire upper surface of the polyimide layer, the liquid repellent coat layer is selectively removed only in a predetermined area, so that the upper surface is removed except for the target application area. The liquid repellent coating layer is formed on the surface. As a means for selectively removing the liquid repellent coating layer, there is a technique in which a laser ablation method is applied to irradiate only the target application region with laser light to selectively evaporate the liquid repellent coating layer.

Further, an alkaline aqueous solution is selectively applied as a surface treatment agent to a desired application region on the upper surface of the polyimide layer, and the imide ring is partially opened to modify the surface of the polyimide layer in the region. Thus, there is a technique for increasing the affinity for the metal nanoparticle dispersion (see Patent Document 4).
Japanese Patent No. 3900388 JP 2005-93814 A Japanese Patent No. 3764349 JP 2006-287217 A

  For example, when a photosensitive polyimide is employed as an interlayer insulating layer that insulates and separates an upper wiring layer and a lower wiring layer in a build-up substrate manufacturing process, a via hole provided in the interlayer insulating layer can be easily manufactured. Specifically, compared to the conventional laser / via method used for producing a via hole, a positive photosensitive polyimide is used to solubilize a light-exposed portion and then remove it by development. Thus, the shape and depth of the via hole to be formed can be easily controlled.

  The entire process includes a step of developing after light exposure and a step of embedding a metal layer in the via hole. In addition, in the step of embedding the metal layer in the via hole, when applying a technique for producing a sintered layer of metal nanoparticles using a metal nanoparticle dispersion, conventionally, using a heating furnace, A method of heating to a predetermined temperature is used. In other words, it is necessary to heat the entire build-up substrate to be manufactured to a predetermined temperature.

  Actually, the region where the heat treatment is necessary is only the portion where the metal nanoparticle dispersion is applied. Considering this point, metal nanoparticles that can be formed by embedding a sintered body layer of metal nanoparticles in the via hole by locally heat-treating only the coating layer portion of the metal nanoparticle dispersion liquid. A proposal of a method for forming a sintered body film is desired. That is, a metal nanoparticle sintered body film in which only a region corresponding to an opening of a target via hole is locally heated and a sintered body layer of metal nanoparticles can be embedded in the via hole. The proposal of the formation method of this is desired.

  Further, on a substrate coated with a polyimide layer, coated with a liquid repellent coating layer, and a metal substrate coated with a liquid repellent coating layer, for example, a conductor layer composed of metallic copper In addition, a proposal of a method for selectively producing a highly adhesive metal nanoparticle sintered body film is desired. In particular, when a high adhesion metal nanoparticle sintered body film is selectively produced, a laser beam is applied only to a target region as a means of heating the metal nanoparticle dispersion liquid to form a metal nanoparticle sintered body film. A proposal of a method that applies a method of performing selective heating by irradiation is desired.

  The present invention solves the above problems. The purpose of the present invention is to apply a technique of condensing laser light and irradiating with a minute spot diameter as means for locally heating only the target region, and only the coating layer portion of the metal nanoparticle dispersion liquid is applied. An object of the present invention is to provide a method for selectively producing a metal nanoparticle sintered body film exhibiting high adhesion to the underlying substrate surface by locally performing heat treatment.

  When using a positive photosensitive polyimide film as the interlayer insulating layer, the positive photosensitive film is used to suppress the phenomenon that the coating liquid layer of the metal nanoparticle dispersion liquid wets and spreads around the opening of the formed via hole. A liquid repellent coating layer is formed on the surface of the conductive polyimide film. When the positive photosensitive polyimide film is exposed to light and then subjected to development processing, the liquid repellent coating layer in the portion is removed together with the solubilized photosensitive polyimide film in the opening. As a result, around the opening of the via hole, the surface of the photosensitive polyimide film is covered with a liquid repellent coating layer to prevent wetting and spreading of the coating layer of the metal nanoparticle dispersion.

  On the substrate coated with the polyimide layer coated with the liquid repellent coating layer, and the substrate having a conductor layer composed of metal copper, for example, metallic copper, coated with the liquid repellent coating layer. The inventors of the present invention have made extensive studies on a method for selectively producing a highly adhesive metal nanoparticle sintered body film.

  For example, when a coating liquid layer of a metal nanoparticle dispersion is formed on a substrate coated with a polyimide layer, which is coated with a liquid repellent coating layer, and laser light of a specific wavelength is irradiated from the surface, It has been found that it is possible to remove the liquid coating layer and to modify the surface of the polyimide layer.

  After that, as a means for selectively removing the coating molecule covering the surface of the metal nanoparticles contained in the coating solution layer of the metal nanoparticle dispersion, it causes specific absorption of the metal nanoparticles. It has also been found that laser light irradiation with a specific wavelength that can be used is available. At that time, when the coating molecules covering the surface of the metal nanoparticles are selectively removed, the metal nanoparticles are adhered to the surface-modified polyimide layer with high adhesion. I also confirmed that.

  The metal nanoparticles from which the surface coating molecules are removed are two-dimensionally deposited on the surface-modified polyimide layer, and further, a layer structure in which the metal nanoparticles are laminated thereon is formed, and then the metal It was confirmed that when laser light having a wavelength absorbed by the nanoparticles was irradiated, low-temperature sintering of the layer in which the metal nanoparticles were laminated proceeded, and a highly adhesive metal nanoparticle sintered body film was selectively formed.

  The step of selectively forming the metal nanoparticle sintered body film by applying the above three types of laser light irradiation is a conductive substrate composed of a metal substrate, for example, metal copper, coated with a liquid repellent coating layer. It was verified that the present invention can also be used for selectively producing a highly adhesive metal nanoparticle sintered body film on a substrate having a body layer.

  The present inventors have completed the present invention based on the above series of findings.

That is, the method for forming a highly adhesive metal nanoparticle sintered body film according to the present invention is as follows.
A method of forming a highly adhesive metal nanoparticle sintered body film on a substrate,
Step 1 to Step 4 below:
(Process 1)
Applying a metal nanoparticle dispersion liquid in a predetermined planar shape on a substrate coated with a liquid repellent coating layer to produce a coating liquid layer;
(Process 2)
Irradiating a laser beam having a wavelength λ ₁ from the surface of the coating liquid layer with an average laser beam intensity P ₁ from a vertical direction (incident angle 0 °);
(Process 3)
After the step 2, a step of irradiating the surface of the coating liquid layer with a laser beam having a wavelength λ ₂ from the vertical direction (incident angle 0 °) with an average laser beam intensity P ₂ ;
(Process 4)
After the step 3, the step of irradiating a laser beam having a wavelength λ ₃ from the surface of the coating solution layer with an average laser beam intensity P ₃ from the vertical direction (incident angle 0 °),
The metal nanoparticle dispersion is
An average particle diameter is selected in the range of 1 to 100 nm, a metal nanoparticle dispersion liquid in which metal nanoparticles are dispersed in a dispersion solvent,
The metal nanoparticles contained in the dispersion can be coordinately bonded to metal atoms on the surface of the metal nanoparticles using lone electron pairs on nitrogen, oxygen, and sulfur atoms. The surface of the metal nanoparticles is coated with an organic compound having a boiling point of 150 ° C. or higher as a coating agent molecule,
The dispersion solvent is a nonpolar organic solvent having a boiling point of 150 ° C. or higher or a low polarity organic solvent,
In the dispersion, when the volume ratio of the metal nanoparticles contained is V _particle volume%, the thickness d of the coating solution layer satisfies 0.5 μm ≧ d · (V _particle / 100). Is selected;
Laser light having a wavelength lambda ₁ is not substantially absorbed into the metal nanoparticles have a wavelength lambda ₁ to be absorbed in the material constituting the surface of said substrate,
When adopting a substrate made of insulating resin material,
Mean laser beam intensity P ₁ is selected in the range of ^{50W / mm 2 ~800W / mm 2} ,
When adopting a substrate made of metal material,
The average laser light intensity P ₁ is selected in the range of 5,000 W / mm ^{2 to} 15,000 W / mm ² ;
Laser light having a wavelength lambda ₂ has a wavelength lambda ₂ to be absorbed by the metallic nanoparticles,
When adopting a substrate made of insulating resin material,
Mean laser beam intensity P ₂ is selected within the range of ^{5W / mm 2 ~200W / mm 2} ,
When adopting a substrate made of metal material,
Mean laser beam intensity P ₂ is selected within the range of ^{500W / mm 2 ~3,000W / mm 2} ;
Laser light having a wavelength lambda ₃ has a wavelength lambda ₃ that is absorbed by the metal constituting the metal nanoparticles,
When adopting a substrate made of insulating resin material,
Mean laser beam intensity P ₃ is selected in the range of ^{5W / mm 2 ~200W / mm 2} ,
When adopting a substrate made of metal material,
Mean laser beam intensity P ₃ is a method for forming a highly adhesive metal nanoparticle sintered body film, which is selected in the range of ^{500W / mm 2 ~3,000W / mm 2} .

At that time, after the step of preparing the coating liquid layer in (Step 1), prior to (Step 2),
It is desirable to provide a pre-drying treatment step for pre-drying the coating liquid layer.

Moreover, the first form of the method for forming a highly adhesive metal nanoparticle sintered body film according to the present invention is the above-described method for forming a highly adhesive metal nanoparticle sintered body film according to the present invention.
The substrate is a substrate coated with a polyimide layer;
The material constituting the surface of the substrate is applied to the polyimide layer.

Further, the second form of the method for forming a highly adhesive metal nanoparticle sintered body film according to the present invention is the above-described method for forming a highly adhesive metal nanoparticle sintered body film according to the present invention.
The substrate is a substrate having a conductor layer made of metallic copper or a copper alloy having a copper content of 97% by mass or more,
The material which comprises the surface of this board | substrate is applied to the form which is a conductor layer comprised with the said metallic copper.

In the first embodiment of the method for forming a highly adhesive metal nanoparticle sintered body film according to the present invention,
The metal nanoparticles are silver nanoparticles,
Laser light having a wavelength lambda ₁ is a Nd / YAG laser beam having a wavelength lambda ₁ = 1064 nm,
Mean laser beam intensity P ₁ is selected in the range of ^{50W / mm 2 ~800W / mm 2} ;
Laser light having a wavelength lambda ₂ is a harmonic of the Nd / YAG laser beam having a wavelength lambda ₂ = 1064 nm of Nd / YAG laser light or the wavelength lambda ₂ = 532 nm,,
Mean laser beam intensity P ₂ is selected within the range of ^{5W / mm 2 ~200W / mm 2} ;
Laser light having a wavelength lambda ₃ is a Nd / YAG laser beam having a wavelength lambda ₃ = 1064 nm,
Mean laser beam intensity P ₃ can employ a condition that is selected in the range of ^{5W / mm 2 ~200W / mm 2} .

In the second embodiment of the method for forming a highly adhesive metal nanoparticle sintered body film according to the present invention,
The metal nanoparticles are silver nanoparticles,
Laser light having a wavelength lambda ₁ is a Nd / YAG laser beam having a wavelength lambda ₁ = 1064 nm,
The average laser light intensity P ₁ is selected in the range of 5,000 W / mm ^{2 to} 15,000 W / mm ² ;
Laser light having a wavelength lambda ₂ is a harmonic of the Nd / YAG laser beam having a wavelength lambda ₂ = 1064 nm of Nd / YAG laser light or the wavelength lambda ₂ = 532 nm,,
Mean laser beam intensity P ₂ is selected within the range of ^{500W / mm 2 ~3,000W / mm 2} ;
Laser light having a wavelength lambda ₃ is a Nd / YAG laser beam having a wavelength lambda ₃ = 1064 nm,
Mean laser beam intensity P ₃ can employ a condition that is selected in the range of ^{500W / mm 2 ~3,000W / mm 2} .

In the first embodiment of the method for forming a highly adhesive metal nanoparticle sintered body film according to the present invention, and the second embodiment,
Irradiation spot diameter D ₁ of the laser beam of wavelength lambda ₁ is selected in a range of 10 m to 500 m;
Irradiation spot diameter D ₂ of the laser beam having a wavelength lambda ₂ is selected in the range of 10 m to 500 m;
Irradiation spot diameter D ₃ of the laser beam having a wavelength lambda ₃ may select a mode that is selected in the range of 10 m to 500 m. that time,
Irradiation spot diameter D ₁ of the laser beam having a wavelength lambda _1, the irradiation spot diameter D ₂ of the laser beam having a wavelength lambda _2, the irradiation spot diameter D ₃ of the laser beam having a wavelength lambda ₃ are selected D ₁ = D ₂ = D ₃ It is preferable to set it as the aspect made.

In the first embodiment of the method for forming a highly adhesive metal nanoparticle sintered body film according to the present invention, and in the second embodiment,
It is preferable to select an alkylamine having a boiling point of 150 ° C. or higher as the coating agent molecule.

  In the method for forming a highly adhesive metal nanoparticle sintered body film according to the present invention, a metal nanoparticle dispersion liquid with a predetermined coating liquid thickness is applied to a predetermined region on a substrate surface coated with a liquid repellent coating layer. When applying, wettability to the surface is limited, and exudation outside the target region is suppressed. Thereafter, the liquid repellent coating layer in contact with the coating solution layer of the metal nanoparticle dispersion is removed by selectively locally heating the interface between the substrate surface and the coating solution layer by laser light irradiation, and the exposed surface of the substrate is exposed. It is possible to selectively form a highly adhesive metal nanoparticle sintered body film. The high adhesion to the substrate surface is caused by mutual diffusion by attaching metal nanoparticles to the surface of a metal substrate, for example, a copper substrate, and locally raising the temperature using laser light irradiation. This is achieved by forming an alloying region to be formed. Or, for example, in the case of a substrate covered with a polyimide layer, the surface of the polyimide layer is irradiated with a laser beam, and as a result of surface modification by photoactivation, it is generated on the modified surface of the polyimide layer. High adhesion to the substrate surface can be imparted through the interaction between the functional group and the metal nanoparticles.

  Below, the formation method of the highly adhesive metal nanoparticle sintered compact film | membrane concerning this invention is further demonstrated.

  In heating by light irradiation, the temperature of the target substance is increased by causing vibration excitation of the target substance using the energy of the irradiated light. For example, even when the wavelength of the irradiated light does not cause electronic excitation of the target substance, it is possible to raise the temperature when inducing vibrational excitation of the target substance.

  In a metal, when lattice vibration is excited, the temperature of the metal itself is increased. Moreover, in the organic compound, when the molecular vibration of the organic compound is excited, the temperature of the organic compound increases.

  In the case of metal nanoparticles having an average particle size of nano-size, the lattice vibration can be excited by light absorption caused by localized plasmons. In addition, organic compound molecules that are intermolecularly bonded to the surface of the metal nanoparticle via a coordinate bond to the metal element are resolved by the excitation of the lattice vibration of the metal nanoparticle. It is possible to leave. Further, Raman scattering can be caused by localized plasmons localized on the surface of the metal nanoparticles. That is, when Stokes-Raman scattering is caused, vibrational excitation of the organic compound molecule itself occurs.

In the present invention, the metal nanoparticles are irradiated with laser light having a wavelength λ ₂ capable of causing plasmon absorption, thereby selectively heating the metal nanoparticles themselves and using localized plasmons. The thermal excitation of the coating molecules is promoted by the excitation of the coating molecules themselves covering the surface by Raman excitation.

On the other hand, the dispersion solvent molecule itself used for dispersion of the metal nanoparticles coated with the coating molecule does not substantially absorb the laser beam having the wavelength λ ₂ to be irradiated. Therefore, as a result of heating the dispersed metal nanoparticles, the temperature of the surrounding dispersion solvent gradually increases due to the heat conduction process. In other words, for the metal nanoparticles that are locally heated by the laser beam with the wavelength λ ₂ that is irradiated, the surrounding dispersion solvent functions as a thermal reservoir, and suppresses the temperature rise of the metal nanoparticles. . Further, when the surface temperature of the coating liquid layer of the metal nanoparticle dispersion rises and approaches the boiling point of the dispersion solvent, transpiration of the dispersion solvent molecules proceeds from the surface. As a result, heat energy converted from the laser light having the wavelength λ ₂ absorbed by the metal nanoparticles is consumed as the evaporation heat. That is, the rapid increase in the surface temperature of the coating solution layer of the metal nanoparticle dispersion is suppressed by the transpiration of the dispersion solvent molecules, and at least the temperature in the vicinity of the surface of the coating solution layer of the metal nanoparticle dispersion is It is controlled within a range not exceeding the boiling point of.

  In the method for forming a highly adhesive metal nanoparticle sintered body film of the present invention, a process comprising the following four steps is used.

(Step 1) Step of forming the coating solution layer of the metal nanoparticle dispersion:
A liquid repellent coating layer for the dispersion solvent contained in the metal nanoparticle dispersion is coated on the surface of the substrate. A metal nanoparticle dispersion liquid is applied in a predetermined pattern shape on the surface of the substrate coated with the liquid repellent coating layer to form a coating liquid layer of the metal nanoparticle dispersion liquid. The thickness d of the coating solution layer of the metal nanoparticle dispersion is such that d · (V / 100) is 0 when the volume ratio of the metal nanoparticles contained in the coating solution layer is V _particle volume%. Select within a range not exceeding 5 μm.

  At that time, since the wettability of the dispersion solvent is low on the substrate surface coated with the liquid repellent coating layer, the applied metal nanoparticle dispersion liquid suppresses the phenomenon of wetting and spreading outside the target pattern shape. Is made.

  The liquid repellent coating layer used for the above purpose suppresses wetting and spreading, and also prevents the metal nanoparticle dispersion from coming into direct contact with the substrate surface.

  Therefore, only the liquid repellent coating layer that exists immediately below the coating solution layer of the metal nanoparticle dispersion and is in contact with the coating solution layer is selectively removed by the first laser light irradiation step of the next step 2. .

(Step 2) First laser beam irradiation step:
When irradiating a laser beam with a wavelength λ ₁ that is difficult to cause plasmon absorption in the metal nanoparticle, a part of the laser beam with a wavelength λ ₁ irradiated to the metal nanoparticle is on the surface of the metal nanoparticle. , Reflected, or scattered. In this case, the light intensity reaching the interface between the coating liquid layer and the substrate depends on the attenuation coefficient A _scatter (λ ₁ ) due to reflection and scattering by the metal nanoparticles: exp {− (A _scatter (λ ₁ ) Decrease in proportion to C _particle ) · d}. Therefore, of the irradiated laser light having the wavelength λ ₁ , the ratio of light that passes through the coating liquid layer of the metal nanoparticle dispersion and reaches the interface between the coating liquid layer and the substrate (apparent light transmittance): T _1-upper (λ ₁ ) is proportional to exp {− (A _scatter (λ ₁ ) · C _particle ) · d}.

On the surface of the coating liquid layer of the metal nanoparticle dispersion liquid, a part of the laser beam having the wavelength λ ₁ to be irradiated is reflected when moving from the gas phase to the liquid phase of the dispersion solvent. The reflectance R _1-upper (λ ₁ ) on the surface does not absorb light with respect to the irradiated laser beam, so the refractive index n _solvent of the dispersed solvent at the wavelength λ ₁ of the laser beam. (Λ ₁ ) and the refractive index n _v (λ ₁ ) of the gas phase (eg, air).

The laser light of wavelength λ ₁ that has passed through the coating liquid layer of the metal nanoparticle dispersion and reached the interface between the coating liquid layer and the substrate, the refractive index also changes discontinuously at the interface between the coating liquid layer and the substrate. Because there is a reflection. At that time, when the material constituting the substrate exhibits absorption with respect to the laser beam having the wavelength λ ₁ , the reflectance R _1-lower (λ ₁ ) at the interface is the absorption rate of the material constituting the substrate. It depends heavily. Further, the ratio of light penetrating into the material constituting the substrate (effective transmittance): T _1-lower (λ ₁ ) also greatly depends on the absorption rate of the material constituting the substrate. When the material constituting the substrate shows a large absorption rate with respect to the laser light having the wavelength λ ₂ , the light entering the material constituting the substrate is absorbed. The ratio of light absorbed by the material constituting the substrate (effective light absorption rate): A _1-lower (λ ₁ ) corresponds to T _1-lower (λ ₁ ).

From the surface of the coating layer of the metal nanoparticle dispersion liquid, a laser beam having a wavelength λ ₁ is applied in the vertical direction (incident angle 0) with an irradiation spot diameter D ₁ (μm) and an average laser beam intensity P ₁ (W / mm ² ). Irradiate from (°). Of the irradiated laser light having the wavelength λ ₁ , a portion corresponding to T _{1 -lower} (λ ₁ ) · P ₁ (W / mm ² ) enters the material constituting the substrate and is absorbed. At that time, a part of the laser beam having the wavelength λ ₁ absorbed by the material constituting the substrate is converted into thermal energy. As a result, in the region irradiated with the laser beam, the temperature of the coating liquid layer / substrate interface is To rise. The temperature of the interface rises from the time of disclosure of laser light irradiation, the irradiation time elapses, and a constant temperature depending on T _{1 -lower} (λ ₁ ) · P ₁ (W / mm ² ): T _1- It reaches _bottom (° C) and reaches an equilibrium state. Specifically, when the irradiation time t ₁ exceeds t ₁ -min, the temperature of the interface reaches approximately T _{1 -bottom} (° C.), and thereafter, the thermal equilibrium state is reached.

Since the liquid repellent that constitutes the liquid repellent coating layer increases in temperature and solubility in the dispersion solvent increases, the temperature of the interface reaches a constant T _{1 -bottom} (° C.). When the time: Δt _{1 is} maintained, the liquid repellent coating layer is dissolved and removed. Therefore, when the total irradiation time t ₁ exceeds (t _1−min + Δt ₁ ), the selective application of the liquid repellent coating layer present at the coating liquid layer / substrate interface in the region irradiated with the laser light is performed. Removal is done. As a result, in the region irradiated with the laser beam, the coating liquid layer of the metal nanoparticle dispersion is in direct contact with the surface of the substrate.

Of course, the temperature of the surface of the coating liquid layer of the metal nanoparticle dispersion also rises as the irradiation time elapses, and the average laser light intensity P ₁ (W / mm ² ) irradiated on the surface of the coating liquid layer is increased. Reliable constant temperature: T _{1 -top} (° C.) is reached and equilibrium is reached. At that time, since the absorption of the laser beam having the wavelength λ ₁ in the coating liquid layer of the metal nanoparticle dispersion liquid is slight, the temperature of the coating liquid layer / substrate interface is higher than the surface of the coating liquid layer. , T _1-bottom (° C.)> T _{1 -top} (° C.).

That is, when the total irradiation time t ₁ exceeds (t _1−min + Δt ₁ ), a temperature gradient is formed in the coating liquid layer from the coating liquid layer / substrate interface toward the surface of the coating liquid layer. The average temperature gradient is (T _{1 -bottom−} T _{1 -top} ) / d (° C./μm).

  After selectively removing the liquid repellent coating layer, in the next step 3: the second laser light irradiation step, the release of the coating molecules covering the surface of the metal nanoparticles and the coating molecular layer were removed. A process of attaching and laminating metal nanoparticles to the substrate surface is performed.

(Step 3) Second laser beam irradiation step:
When laser light with a wavelength λ ₂ capable of causing plasmon absorption is irradiated on the metal nanoparticles from the surface of the coating liquid layer of the metal nanoparticle dispersion, a part of the plasmon absorption of the metal nanoparticles causes It is converted into thermal energy or used for thermal detachment of the coating molecules on the surface of the metal nanoparticles. Furthermore, a part is reflected or scattered by the metal nanoparticle surface. As a result, from the surface of the coating liquid layer of the metal nanoparticle dispersion liquid, the laser light having the wavelength λ ₂ is transmitted through the coating liquid layer of the metal nanoparticle dispersion liquid, and the coating liquid of the metal nanoparticle dispersion liquid The light intensity reaching the interface between the layer and the substrate decreases depending on the dispersion concentration C _particle of the metal nanoparticles dispersed in the dispersion and the thickness d of the coating liquid layer. Specifically, the light intensity reaching the interface between the coating liquid layer and the substrate is determined by the absorption coefficient A _plasmon (λ ₂ ) due to plasmon absorption by the metal nanoparticles, and the attenuation coefficient A _scatter due to reflection and scattering (A _scatter ( depends on _{λ 2), exp [- {} (a plasmon (λ 2) + a scatter (λ 2)) · C particle} · d] in proportion to the decreases. Therefore, of the irradiated laser light of wavelength λ ₂ , the ratio of light that passes through the coating liquid layer of the metal nanoparticle dispersion and reaches the interface between the coating liquid layer and the substrate (apparent light transmittance): T _2-upper (λ ₂ ) is proportional to exp [− {(A _plasmon (λ ₂ ) + A _scatter (λ ₂ )) · C _particle } · d].

On the surface of the coating liquid layer of the metal nanoparticle dispersion liquid, a part of the laser beam with the wavelength λ ₂ to be irradiated is reflected when moving from the gas phase to the liquid phase of the dispersion solvent. The reflectance R _{2 -upper} (λ ₂ ) on the surface does not absorb light with respect to the irradiated laser beam, so the refractive index n _solvent of the dispersion solvent at the wavelength λ ₂ of the laser beam. (Λ ₂ ) and the refractive index n _v (λ ₂ ) of the gas phase (eg, air).

Laser light of wavelength λ ₂ that has passed through the coating liquid layer of the metal nanoparticle dispersion and reached the interface between the coating liquid layer and the substrate, the refractive index also changes discontinuously at the interface between the coating liquid layer and the substrate. Because there is a reflection. At that time, when the material constituting the substrate exhibits absorption with respect to the laser beam having the wavelength λ ₂ , the reflectance R _2-lower (λ ₂ ) at the interface is the absorption rate of the material constituting the substrate. It depends heavily. Further, the ratio of light penetrating into the material constituting the substrate (effective transmittance): T _2-lower (λ ₂ ) also greatly depends on the absorption rate of the material constituting the substrate. When the material constituting the substrate shows a large absorption rate with respect to the laser light having the wavelength λ ₂ , the light entering the material constituting the substrate is absorbed. The ratio of light absorbed by the material constituting the substrate (effective light absorption rate): A _2-lower (λ ₂ ) corresponds to T _2-lower (λ ₂ ).

From the surface of the coating layer of the metal nanoparticle dispersion liquid, a laser beam having a wavelength λ ₂ is applied in the vertical direction (incident angle 0) with an irradiation spot diameter D ₂ (μm) and an average laser beam intensity P ₂ (W / mm ² ). Irradiate from (°). Of the irradiated laser light having the wavelength λ ₂ , a portion corresponding to T _{2 -lower} (λ ₂ ) · P ₂ (W / mm ² ) enters the material constituting the substrate and is absorbed. At that time, a part of the laser beam having the wavelength λ ₂ absorbed by the material constituting the substrate is converted into thermal energy. As a result, in the region irradiated with the laser beam, the temperature of the coating liquid layer / substrate interface is To rise. The temperature of the interface rises from the time of disclosure of laser light irradiation, the irradiation time elapses, and a constant temperature depending on the T _2-lower (λ ₂ ) · P ₂ (W / mm ² ): T ₂₋ It reaches _bottom (° C) and reaches an equilibrium state. Specifically, when the irradiation time t ₂ exceeds t _2−min , the temperature of the interface reaches approximately T _2−bottom (° C.), and thereafter, the thermal equilibrium state is reached.

On the other hand, the laser light having the wavelength λ ₂ is absorbed by the metal nanoparticles dispersed in the coating liquid layer, and localized plasmons are generated on the surface thereof. Along with the absorption of the laser beam having the wavelength λ ₂ , the lattice vibration of the metal nanoparticles is excited, and the metal nanoparticles are locally heated. By the absorption by the metal nanoparticles, the laser light having the wavelength λ ₂ is converted into heat energy, and further, heat energy is provided through heat conduction to the dispersion solvent around the metal nanoparticles. As a result, the temperature of the coating liquid layer also rises, but when the irradiation time t ₂ exceeds t _{2 -min} , a thermal quasi-equilibrium state is thereafter obtained. For example, the temperature of the surface of the coating liquid layer of the metal nanoparticle dispersion rises as the irradiation time elapses, and reaches the average laser light intensity P ₂ (W / mm ² ) irradiated onto the surface of the coating liquid layer. Reliable constant temperature: T _{2 -top} (° C.) is reached and a quasi-equilibrium state is reached.

At that time, if the thickness d of the coating solution layer is selected in a range where d · (V / 100) does not exceed 0.5 μm, it is usually T _{2 -bottom} (° C.)> T _{2 -top} (° C.). Become.

When localized plasmons are generated on the surface of the metal nanoparticles, the localized plasmons cause vibrational excitation of the coating molecules on the surface of the metal nanoparticles. In that state, the thermal detachment of the coating agent molecule is promoted from the surface of the metal nanoparticle. Therefore, even in the vicinity of the coating liquid layer / substrate interface, the thermal detachment of the coating molecules proceeds from the surface of the metal nanoparticles, and the metal nanoparticles from which the coating molecules have been removed adhere to the substrate surface, The attached metal nanoparticles form a two-dimensional layer structure. The adhesion layer of the two-dimensional metal nanoparticles is used as a nucleation layer, and metal nanoparticles from which the coating agent molecules are removed are laminated on the upper surface. During the lamination of the metal nanoparticles, the metal nanoparticles are heated to about T _{2 -bottom} (° C.), and the metal nanoparticles are in a fused state.

When the temperature of the interface reaches T _{2 -bottom} (° C.), when laser light irradiation is continued for a certain time: Δt _2, the metal nanoparticles contained in the coating liquid layer are transferred to the stack of metal nanoparticles. It is taken in. As a result, the surface of the coating liquid layer is coated with the coating agent molecules, and the dispersed metal nanoparticles are not substantially left. Therefore, when the total irradiation time t ₂ exceeds (t _2−min + Δt ₂ ), in the region irradiated with the laser light, a stack of metal nanoparticles is attached to the surface of the substrate.

  In the process, the transpiration of the dispersion solvent molecules and coating molecules gradually proceeds from the surface of the coating liquid layer, but a sufficient amount of dispersion solvent remains to immerse the entire laminated structure of metal nanoparticles. It has become.

  The layer in which the metal nanoparticles are adhered densely attached to the surface of the substrate is subjected to low temperature sintering by the following step 4: third laser light irradiation step, and the metal nanoparticle sintered body film and To do.

(Step 4) Third laser beam irradiation step:
The coating molecules that coat the surface of the metal nanoparticles are detached, and when the metal nanoparticles are deposited to cover the substrate surface, a layer in which the metal nanoparticles are densely stacked is irradiated. Laser light is shielded by a layer in which the metal nanoparticles are densely stacked.

In this state, when the laser beam having the wavelength λ ₃ is irradiated from the surface of the coating solution layer, the laser beam having the wavelength λ ₃ that has entered the coating solution layer is dispersed solvent molecules, and the coating agent dissolved in the dispersion solvent. When not absorbed by the molecules, the light passes through the coating solution layer and enters the layer in which the metal nanoparticles are densely stacked.

On the surface of the coating liquid layer, a part of the laser beam with the wavelength λ ₃ to be irradiated is reflected when moving from the gas phase to the liquid phase of the dispersion solvent. Reflectance R _3-upper in the surface (lambda _3), to the laser beam irradiated, dispersing agent molecules, the dispersion solvent shows no optical absorption, at the wavelength lambda ₃ of the laser beam, the dispersion solvent It depends on the refractive index n _solvent (λ ₃ ) and the refractive index n _v (λ ₃ ) of the gas phase (eg, air).

Actually, the metal nanoparticles dispersed in the coating liquid layer do not remain, but for example, scattering and Raman scattering by the dispersant molecules dissolved in the dispersion solvent exist, When passing through, the intensity of the laser light of wavelength λ ₃ is slightly attenuated. Therefore, the ratio of the light that passes through the coating liquid layer and reaches the surface of the densely layered metal nanoparticles, that is, the apparent transmittance of the coating liquid layer: T _3-upper (λ ₃ ) is attenuation coefficient due to light absorption, reflection and scattering in the liquid layer: depends on _{a scatter (λ 3), exp} {- (a scatter (λ 3) · d} in proportion to the decreases.

The metal constituting the metal nanoparticles, by the surface plasmon absorption, if it is possible to absorb a laser beam having a wavelength lambda _3, the laser wavelength lambda ₃ which metal nanoparticles are incident on the layers that are closely stacked Part of the light is absorbed. Of course, reflection or scattering of the laser light having the wavelength λ ₃ also occurs on the surface of the layer in which the metal nanoparticles are densely stacked. The apparent reflectance R _{3 metal-layer} (λ ₃ ) on the surface of the layer in which the metal nanoparticles are densely laminated depends on the absorption rate of the layer in which the metal nanoparticles are densely laminated. In addition, the ratio of light penetrating into the layer in which the metal nanoparticles are densely stacked (effective transmittance): T _{3 -metal-layer} (λ ₃ ) also depends on the absorption rate of this layer.

When the layer in which the metal nanoparticles are densely laminated exhibits a large absorption rate for the laser light having the wavelength λ ₃ , the light that enters the layer in which the metal nanoparticles are densely laminated is absorbed. Ratio of light absorbed by the layer in which the metal nanoparticles are densely stacked (effective light absorption rate): A _{3-metal-layer} (λ ₃ ) is equivalent to T _{3-metal-layer} (λ ₃ ) is doing.

At that time, the laser light having a wavelength of λ ₃ absorbed by the layer in which the metal nanoparticles are densely stacked generates, for example, surface plasmons and further causes excitation of lattice vibration, thereby causing each metal nanoparticle to be excited. Heat locally. At that time, in the layer of the layer in which the metal nanoparticles are densely stacked, in each metal nanoparticle, the thermal energy converted from the laser light having the wavelength λ ₃ is made uniform throughout the layer through heat conduction. Is done. Of course, thermal energy is also supplied to the dispersion solvent existing around the densely layered layer of metal nanoparticles through heat conduction, and heating is performed.

In other words, for the layer in which the metal nanoparticles are densely stacked, which is locally heated by the laser beam of wavelength λ ₃ to be irradiated, the surrounding dispersion solvent functions as a thermal reservoir, and a rapid temperature The rise is suppressed. Further, when the surface temperature of the coating liquid layer rises and approaches the boiling point of the dispersion solvent, the dispersion solvent molecules evaporate from the surface. As a result, thermal energy converted from the laser light having the wavelength λ ₃ absorbed by the layer in which the metal nanoparticles are densely stacked is consumed as the evaporation heat. That is, the rapid increase in the surface temperature of the coating liquid layer is suppressed by the transpiration of the dispersion solvent molecules, and at least the temperature near the surface of the coating liquid layer is controlled in a range not exceeding the boiling point of the dispersion solvent.

From the surface of the coating liquid layer, a laser beam having a wavelength λ ₃ is irradiated from the vertical direction (incident angle 0 °) with an irradiation spot diameter D ₃ (μm) and an average laser beam intensity P ₃ (W / mm ² ). Of the irradiated laser light of wavelength λ ₃ , the part corresponding to T _{3-metal-layer} (λ ₃ ) · P ₃ (W / mm ² ) enters the layer in which metal nanoparticles are densely stacked. And absorbed. At that time, the laser light of wavelength λ ₃ absorbed by the layer in which the metal nanoparticles are densely laminated is converted into thermal energy. As a result, the metal nanoparticles are densely laminated in the region irradiated with the laser light. The temperature of the layer increases. The temperature of the interface rises from the time of disclosure of laser light irradiation, the irradiation time elapses, and a constant temperature depending on the T _{3-metal-layer} (λ ₃ ) · P ₃ (W / mm ² ): T It reaches _3-bottom (° C) and becomes a quasi-equilibrium state. Specifically, when the irradiation time t ₃ exceeds t _{3 -min} , the temperature of the layer in which the metal nanoparticles are densely stacked reaches approximately T _{3 -bottom} (° C.), and then the thermal It becomes a quasi-equilibrium state.

Further, the temperature of the surface of the coating liquid layer rises as the irradiation time elapses, and is a constant temperature that depends on the average laser light intensity P ₃ (W / mm ² ) irradiated on the surface of the coating liquid layer: T _{3 -top} (° C.) is reached and a pseudo-equilibrium state is reached. At this stage, light absorption in the coating liquid layer is substantially absent, and heating is performed by thermal energy supplied by heat conduction from a layer in which metal nanoparticles are densely stacked. Therefore, T _3-bottom (° C.)> T _3-top (° C.).

As a result of being maintained at the above temperature, low-temperature sintering proceeds in a layer in which metal nanoparticles are densely stacked. When the temperature reaches T _{3 -bottom} (° C.) and the laser beam irradiation is continued for a certain time: Δt ₃ , it is converted into a metal nanoparticle sintered body film. Accordingly, when the total irradiation time t ₃ exceeds (t _3−min + Δt ₃ ), a highly adhesive metal nanoparticle sintered body film is formed on the surface of the substrate in the region irradiated with the laser beam. It becomes a state.

  In the process, evaporation of the dispersion solvent molecule, the coating agent molecule, and the liquid repellent molecule proceeds from the surface of the coating liquid layer, and finally the dispersion solvent molecule, the coating agent molecule, and the liquid repellent molecule are not left.

  In the method for forming a highly adhesive metal nanoparticle sintered body film according to the present invention, in step 2 and step 3, the liquid repellent molecule and the coating agent molecule are eluted in the dispersion solvent contained in the coating liquid layer. Therefore, in the process 1, after forming the coating liquid layer of the metal nanoparticle dispersion liquid, a form in which a drying process for removing most of the dispersion solvent contained in the coating liquid layer is not performed is preferable.

(Pre-drying process)
On the other hand, after the step 1 and before the step 2, the content ratio of the dispersion solvent contained in the coating solution layer of the metal nanoparticle dispersion does not interfere with the elution of the liquid repellent molecule and the coating agent molecule. It is also possible to provide a preliminary drying treatment step in which the dispersion solvent contained in the coating liquid layer is partially removed by transpiration. In this preliminary drying process, the dispersion liquid contained in the coating liquid layer is partially removed by evaporation by heating the entire coating liquid layer to a temperature T _prebaking (° C.). At that time, the temperature T _prebaking (° C.) of the pre-drying treatment is compared with the temperature achieved by the first laser light irradiation step of the above step 2, T _{1 -bottom} (° C.)> T _{1 -top} (° C.). And at least the range of T _{1 -bottom} (° C.)> T _prebaking (° C.), preferably 1/2 {T _{1 -bottom} (° C.) + T _{1 -top} (° C.)} ≧ T _prebaking (° C.) Select to range.

Specifically, the temperature T _prebaking (° C.) of the pre-drying treatment is generally in the range of 120 ° C.> T _prebaking (° C.), preferably in the range of 110 ° C. ≧ T _prebaking (° C.) ≧ 50 ° C., desirably A range of 100 ° C. ≧ T _prebaking (° C.) ≧ 60 ° C. is selected. The heating time t _prebaking of the preliminary drying treatment is appropriately selected according to the boiling point of the dispersion solvent partially evaporated, the content ratio thereof, and the temperature T _prebaking (° C.). For example, when the temperature T _prebaking (° C.) is selected in the range of 100 ° C. ≧ T _prebaking (° C.) ≧ 60 ° C., the heating time t _prebaking is in the range of 30 seconds to 600 seconds, usually 60 seconds to 300 seconds. It is desirable to select a range of seconds.

  As a result of the preliminary drying treatment, the volume ratio of the dispersion solvent contained in the coating liquid layer is reduced. As a result, the amount of the dispersed solvent that evaporates is relatively decreased with the heating by the laser beam irradiation. When using a dispersion solvent with a relatively low ignition point, reducing the amount of transpiration of the dispersion solvent prevents it from being locally heated by laser light irradiation in the atmosphere and satisfying the ignition conditions. There is also an effect.

  In the method for forming a highly adhesive metal nanoparticle sintered body film according to the present invention, in the first embodiment, a substrate covered with a polyimide layer is employed as the substrate.

At that time, in the “first laser light irradiation step” of step 2 in which the liquid repellent coating layer that coats the surface of the polyimide layer is removed, a step of irradiating with the laser light having the wavelength λ ₁ and absorbing it by the polyimide layer Is used to modify the surface of the polyimide layer.

For example, in step 2, the polyimide layer itself exhibits optical absorption with respect to the harmonics of Nd / YAG laser light having wavelengths λ ₁ = 532 nm, 355 nm, and 266 nm, and undergoes photoactivation due to this optical absorption. Further, the polyimide layer is activated by being locally excited by irradiation with Nd / YAG laser light having a wavelength λ ₁ = 1064 nm. Specifically, modification is performed with photoactivation in the polyimide layer. For example, a partial imide ring opening reaction proceeds in the laser exposure region. By this partial imide ring opening, for example, a —COOH-type functional group derived from an imide ring and a —CO—NH— bond are generated. By the modification of the polyimide layer, for example, a —COOH type functional group or a —CO—NH— bond is formed between the metal nanoparticles, for example, silver atoms on the surface of the silver nanoparticles. It has the function of forming bonds. Therefore, the structure of, for example, —COOH-type functional groups and —CO—NH— bonds produced on the surface of the polyimide layer by modification is the same as metal nanoparticles, for example, silver nanoparticles. By interacting, it exhibits the function of improving adhesion.

  In the first embodiment, it is preferable to select the following conditions in the above-described steps 1 to 4.

  In step 1, the liquid repellent that coats the surface of the polyimide layer is an organic compound that exhibits liquid repellency with respect to the dispersion solvent used in the metal nanoparticle dispersion. For example, a fluorine-based surface treatment agent such as EGC-1720, 3M Novec (Sumitomo 3M Limited), or the like can be used as the liquid repellent. The film thickness of the liquid repellent coating layer is generally selected in the range of 5 nm to 100 nm, preferably in the range of 5 nm to 20 nm. It is desirable that the liquid repellent coating layer be uniformly applied so as to cover the entire surface of the polyimide layer.

The thickness d of the coating solution layer of the metal nanoparticle dispersion is such that d · (V / 100) when the volume ratio of the metal nanoparticles contained in the coating solution layer is V _particle volume%. , And select within a range not exceeding 0.5 μm. In that case, the thickness d of the coating solution layer of the metal nanoparticle dispersion is selected in the range of 1 μm to 5 μm, preferably in the range of 2 μm to 4 μm. On the other hand, the volume ratio of metal nanoparticles contained in the metal nanoparticle dispersion liquid: V _particle volume% is selected in the range of 10 volume% to 50 volume%, preferably 10 volume% to 25 volume%.

As the laser light having the wavelength λ ₁ used in the step 2, for example, when silver nanoparticles are used as the metal nanoparticles, it is preferable to employ Nd / YAG laser light having a wavelength of 1064 nm. Further, when the surface of the coating liquid layer is irradiated from the vertical direction (incident angle 0 °), it is preferable that the laser beam having the wavelength λ ₁ is irradiated with a minute spot diameter via the optical fiber. The irradiation spot diameter D ₁ (μm) is selected in the range of 10 μm to 500 μm, preferably in the range of 100 μm to 500 μm. The average laser beam intensity P ₁ of the laser beam having a wavelength lambda ₁ emitted (W / mm ²⁾ is in the range of 50~800W / mm ^2, preferably, selected within the range of 100 to 500 W / mm ^2.

When continuously irradiating the irradiation spot point with laser light having the wavelength λ ₁ , the irradiation time t ₁ is selected to be at least 1 ms, usually in the range of 1 ms to 100 ms, preferably in the range of 20 ms to 50 ms. Therefore, total dose: P ₁ · t ₁ in the range of 800~20,000W · ms / mm ^2, preferably, selected within the range of 2,000~15,000W · ms / mm ^2.

As the laser light having a wavelength λ ₂ used in step 3, for example, when silver nanoparticles are used as metal nanoparticles, Nd / YAG laser light having a wavelength of 1064 nm, Nd / YAG laser light having a wavelength of 532 nm, and 355 nm are used. It is preferable to employ harmonics. In addition, if the harmonics of Nd / YAG laser light with wavelengths of 532 nm and 355 nm are employed, the contribution of absorption due to the localized plasmons of the silver nanoparticles increases. Instead of the harmonics of the Nd / YAG laser light having the wavelengths of 532 nm and 355 nm, for example, argon ion laser light having the wavelengths of 488 nm and 514.5 nm may be used.

Further, when irradiating the surface of the coating liquid layer from the vertical direction (incident angle 0 °), it is preferable to irradiate the laser light having the wavelength λ ₂ with a minute spot diameter via the optical fiber. The irradiation spot diameter D ₂ (μm) is selected in the range of 10 μm to 500 μm, preferably in the range of 100 μm to 500 μm. The average laser beam intensity P ₂ of the laser beam having a wavelength lambda ₂ emitted (W / mm ²⁾ is in the range of 5~200W / mm ^2, preferably, selected within the range of 10 to 100 W / mm ^2.

When continuously irradiating the irradiation spot point with the laser beam having the wavelength λ ₂ , the irradiation time t ₁ is selected to be at least 1 ms, usually in the range of 1 ms to 100 ms, preferably in the range of 20 ms to 50 ms. Therefore, total dose: P ₂ · t ₂ is in the range of 200~5,000W · ms / mm ^2, preferably, selected within the range of 500~3,000W · ms / mm ^2.

As the laser light having the wavelength λ ₃ used in step 4, for example, when silver nanoparticles are used as the metal nanoparticles, it is preferable to employ Nd / YAG laser light having a wavelength of 1064 nm. Similarly to step 3, the harmonics of Nd / YAG laser beams having wavelengths of 532 nm and 355 nm may be employed as the laser beam having wavelength λ ₃ used in step 4. Instead of the harmonics of the Nd / YAG laser light having the wavelengths of 532 nm and 355 nm, for example, argon ion laser light having the wavelengths of 488 nm and 514.5 nm may be used.

Further, when irradiating the surface of the coating liquid layer from the vertical direction (incident angle 0 °), it is preferable to irradiate the laser beam having the wavelength λ ₃ with a minute spot diameter via the optical fiber. The irradiation spot diameter D ₃ (μm) is selected in the range of 10 μm to 500 μm, preferably in the range of 100 μm to 500 μm. The average laser beam intensity P ₂ of the laser beam having a wavelength lambda ₃ emitted (W / mm ²⁾ is in the range of 5~200W / mm ^2, preferably, selected within the range of 10 to 100 W / mm ^2.

When continuously irradiating the irradiation spot point with the laser beam having the wavelength λ ₃ , the irradiation time t ₁ is selected to be at least 1 ms, usually in the range of 1 ms to 100 ms, preferably in the range of 20 ms to 50 ms. Therefore, total dose: P ₃ · t ₃ is in the range of 200~5,000W · ms / mm ^2, preferably, selected within the range of 500~3,000W · ms / mm ^2.

  In the method for forming a highly adhesive metal nanoparticle sintered body film according to the present invention, in the second embodiment, a metal substrate, for example, a substrate having a metal foil as a conductor layer is employed as the substrate.

In this case, in the “first laser light irradiation step” of step 1 in which the conductive layer of the metal foil, for example, the liquid repellent coating layer that coats the surface of the electrolytic copper conductive layer is removed, the laser having the wavelength λ ₁ Light is irradiated and absorbed by a conductive layer of the metal foil, for example, a conductive layer of electrolytic copper.

  After the step of removing the liquid repellent coating layer, in step 3, metal nanoparticles, for example, silver nanoparticles are attached to the surface of the conductive layer of the metal foil, for example, the conductive layer of electrolytic copper. The Furthermore, in Step 4, by performing a low-temperature sintering treatment, mutual diffusion occurs between the conductive layer of the metal foil, for example, the conductive layer of electrolytic copper, and the metal nanoparticles, for example, silver nanoparticles. proceed. Due to the presence of the alloying region formed by this interdiffusion, a state in which a highly adhesive metal nanoparticle sintered body film is formed on the surface of the conductor layer of the metal foil, for example, the conductor layer of electrolytic copper, and Become.

  In the second embodiment, it is preferable to select the following conditions in the above-described steps 1 to 4.

  In step 1, the liquid repellent that coats the surface of the metal substrate, for example, the conductive layer of electrolytic copper, uses an organic compound that exhibits liquid repellency with respect to the dispersion solvent used in the metal nanoparticle dispersion. For example, a fluorine-based surface treatment agent such as EGC-1720, 3M Novec (Sumitomo 3M Limited), or the like can be used as the liquid repellent. The film thickness of the liquid repellent coating layer is generally selected in the range of 5 nm to 100 nm, preferably in the range of 5 nm to 20 nm. The liquid repellent coating layer is desirably uniformly applied so as to cover the entire surface of a metal substrate, for example, an electrolytic copper conductor layer.

The thickness d of the coating solution layer of the metal nanoparticle dispersion is such that d · (V / 100) when the volume ratio of the metal nanoparticles contained in the coating solution layer is V _particle volume%. , And select within a range not exceeding 0.5 μm. In that case, the thickness d of the coating solution layer of the metal nanoparticle dispersion is selected in the range of 1 μm to 5 μm, preferably in the range of 2 μm to 4 μm. On the other hand, the volume ratio of metal nanoparticles contained in the metal nanoparticle dispersion liquid: V _particle volume% is selected in the range of 10 volume% to 50 volume%, preferably 10 volume% to 25 volume%.

As the laser light having the wavelength λ ₁ used in the step 2, for example, when silver nanoparticles are used as the metal nanoparticles, it is preferable to employ Nd / YAG laser light having a wavelength of 1064 nm. Further, when the surface of the coating liquid layer is irradiated from the vertical direction (incident angle 0 °), it is preferable that the laser beam having the wavelength λ ₁ is irradiated with a minute spot diameter via the optical fiber. The irradiation spot diameter D ₁ (μm) is selected in the range of 10 μm to 500 μm, preferably in the range of 100 μm to 500 μm. The average laser beam intensity P ₁ of the laser beam having a wavelength lambda ₁ emitted (W / mm ²⁾ is in the range of 5,000~15,000W / mm ^2, preferably, 10,000～15,000W / Select in the mm ² range.

When continuously irradiating a laser beam of wavelength λ ₁ to the irradiation spot point, the irradiation time t ₁ is selected to be at least 0.5 ms, usually in the range of 0.5 ms to 10 ms, preferably in the range of 2 ms to 5 ms. To do. Therefore, total dose: P ₁ · t ₁ in the range of 7,500~75,000W · ms / mm ^2, preferably, selected within the range of 20,000~50,000W · ms / mm ^2.

As a laser beam having a wavelength λ ₂ used in step 3, for example, when silver nanoparticles are used as metal nanoparticles, an Nd / YAG laser beam wavelength of 1064 nm, an Nd / YAG laser beam of wavelengths 532 nm and 355 nm is used. It is preferable to employ the higher harmonic. In addition, if the harmonics of Nd / YAG laser light with wavelengths of 532 nm and 355 nm are employed, the contribution of absorption due to the localized plasmons of the silver nanoparticles increases. Instead of the harmonics of the Nd / YAG laser light having the wavelengths of 532 nm and 355 nm, for example, argon ion laser light having the wavelengths of 488 nm and 514.5 nm may be used.

Further, when irradiating the surface of the coating liquid layer from the vertical direction (incident angle 0 °), it is preferable to irradiate the laser light having the wavelength λ ₂ with a minute spot diameter via the optical fiber. The irradiation spot diameter D ₂ (μm) is selected in the range of 10 μm to 500 μm, preferably in the range of 100 μm to 500 μm. The average laser light intensity of the laser beam having a wavelength lambda ₂ emitted P ^₂ (W / mm ₂₎ is in the range of 500~3,000W / mm ^2, preferably, 1,00~2,000W / mm ² Select the range.

When continuously irradiating a laser beam of wavelength λ ₂ to the irradiation spot point, the irradiation time t ₂ is selected to be at least 0.5 ms, usually in the range of 0.5 ms to 10 ms, preferably in the range of ₂ ms to 5 ms. To do. Therefore, total dose: P ₂ · t ₂ is in the range of 1,500~7,500W · ms / mm ^2, preferably, selected within the range of 2,000~5,000W · ms / mm ^2.

As the laser light having the wavelength λ ₃ used in step 4, for example, when silver nanoparticles are used as the metal nanoparticles, it is preferable to employ Nd / YAG laser light having a wavelength of 1064 nm. Similarly to step 3, the harmonics of Nd / YAG laser beams having wavelengths of 532 nm and 355 nm may be employed as the laser beam having wavelength λ ₃ used in step 4. Instead of the harmonics of the Nd / YAG laser light having the wavelengths of 532 nm and 355 nm, for example, argon ion laser light having the wavelengths of 488 nm and 514.5 nm may be used.

Further, when irradiating the surface of the coating liquid layer from the vertical direction (incident angle 0 °), it is preferable to irradiate the laser beam having the wavelength λ ₃ with a minute spot diameter via the optical fiber. The irradiation spot diameter D ₃ (μm) is selected in the range of 10 μm to 500 μm, preferably in the range of 100 μm to 500 μm. The average laser beam intensity P ₃ of the laser beam having a wavelength lambda ₃ emitted (W / mm ²⁾ is in the range of 500~3,000W / mm ^2, preferably, 1,00~2,000W / mm ² Select the range.

When continuously irradiating the irradiation spot point with the laser beam having the wavelength λ ₃ , the irradiation time t ₃ is selected to be at least 0.5 ms or more, usually 0.5 ms to 10 ms, preferably 2 ms to 5 ms. To do. Therefore, total dose: P ₃ · t ₃ is in the range of 1,500~7,500W · ms / mm ^2, preferably, selected within the range of 2,000~5,000W · ms / mm ^2.

  Alternatively, similar conditions can be used for a substrate that employs a conductor layer made of a copper alloy having a copper content of 97% by mass or more.

  In the method for forming a highly adhesive metal nanoparticle sintered body film according to the present invention, first, the above steps 1 to 4 are carried out to show high adhesion to the substrate surface, and the film thickness is about 0.5 μm. The metal nanoparticle sintered body film is formed. Thereafter, a coating liquid layer of the metal nanoparticle dispersion is formed on the metal nanoparticle sintered body, and the same operation as in Step 3 and Step 4 is performed, so that the metal nanoparticle sintered body is sequentially formed. By laminating, it is possible to produce a metal nanoparticle sintered body layer having a large overall film thickness.

  That is, in addition to the above-described Step 1 to Step 4, the following Step 1 ′, Step 3 ′, Step 4 ′ are repeated to laminate a metal nanoparticle sintered body film having a thickness of about 0.5 μm. It is possible to produce a metal nanoparticle sintered body layer having a large overall film thickness.

(Step 1 ′) Step of forming a coating layer of the metal nanoparticle dispersion:
A metal nanoparticle dispersion is applied in a predetermined pattern shape to the surface of the produced metal nanoparticle sintered body film to form a coating liquid layer of the metal nanoparticle dispersion. The thickness d of the coating solution layer of the metal nanoparticle dispersion is such that d · (V / 100) is 0 when the volume ratio of the metal nanoparticles contained in the coating solution layer is V _particle volume%. Select within a range not exceeding 5 μm.

  At that time, since the wettability of the dispersion solvent is low on the substrate surface coated with the liquid repellent coating layer, the applied metal nanoparticle dispersion liquid suppresses the phenomenon of wetting and spreading outside the target pattern shape. Is made.

  On the other hand, since the metal nanoparticle dispersion exhibits good wettability with respect to the surface of the produced metal nanoparticle sintered body film, a coating liquid layer having the same pattern shape can be obtained.

  A second laser light irradiation step of the next step 3 'is performed.

(Step 3 ′) Second laser light irradiation step:
From the surface of the coating layer of the metal nanoparticle dispersion liquid, a laser beam having a wavelength λ ₂ is applied in the vertical direction (incident angle 0) with an irradiation spot diameter D ₂ (μm) and an average laser beam intensity P ₂ (W / mm ² ). Irradiate from (°).

  When localized plasmons are generated on the surface of the metal nanoparticles, the localized plasmons cause vibrational excitation of the coating molecules on the surface of the metal nanoparticles. In that state, the thermal detachment of the coating agent molecule is promoted from the surface of the metal nanoparticle. Therefore, even in the vicinity of the interface of the coating liquid layer / metal nanoparticle sintered body film, the thermal detachment of the coating molecule proceeds from the surface of the metal nanoparticle, and the metal nanoparticle from which the coating molecule is removed, The metal nanoparticles adhered to the surface of the metal nanoparticle sintered body form a two-dimensional layer structure. The adhesion layer of the two-dimensional metal nanoparticles is used as a nucleation layer, and metal nanoparticles from which the coating agent molecules are removed are laminated on the upper surface.

Even during the lamination of the metal nanoparticles, the metal nanoparticles are heated to about T _{2 -bottom} (° C.), and the metal nanoparticles are in a fused state.

  The layer in which the metal nanoparticles are adhered densely attached to the surface of the metal nanoparticle sintered body is subjected to low temperature sintering by the following step 4 ′: third laser light irradiation step, and the metal A nanoparticle sintered body film is used.

(Step 4 ′) Third laser beam irradiation step:
From the surface of the coating liquid layer, a laser beam having a wavelength λ ₃ is irradiated from the vertical direction (incident angle 0 °) with an irradiation spot diameter D ₃ (μm) and an average laser beam intensity P ₃ (W / mm ² ). At that time, the laser light of wavelength λ ₃ absorbed by the layer in which the metal nanoparticles are densely laminated is converted into thermal energy. As a result, the metal nanoparticles are densely laminated in the region irradiated with the laser light. The temperature of the layer increases. Specifically, when the irradiation time t ₃ exceeds t _{3 -min} , the temperature of the layer in which the metal nanoparticles are densely stacked reaches approximately T _{3 -bottom} (° C.), and then the thermal It becomes a quasi-equilibrium state.

Further, the temperature of the surface of the coating liquid layer rises as the irradiation time elapses, and is a constant temperature that depends on the average laser light intensity P ₃ (W / mm ² ) irradiated on the surface of the coating liquid layer: T _{3 -top} (° C.) is reached and a pseudo-equilibrium state is reached. At this stage, light absorption in the coating liquid layer is substantially absent, and heating is performed by thermal energy supplied by heat conduction from a layer in which metal nanoparticles are densely stacked. Therefore, T _3-bottom (° C.) ≧ T _3-top (° C.).

As a result of being maintained at the above temperature, low-temperature sintering proceeds in a layer in which metal nanoparticles are densely stacked. When the temperature reaches T _{3 -bottom} (° C.) and the laser beam irradiation is continued for a certain time: Δt ₃ , it is converted into a metal nanoparticle sintered body film. Accordingly, when the total irradiation time t ₃ exceeds (t _3−min + Δt ₃ ), a highly adhesive metal nanoparticle sintered body film is formed on the surface of the substrate in the region irradiated with the laser beam. It becomes a state.

  In the process, the transpiration of the dispersion solvent molecules and the coating agent molecules proceeds from the surface of the coating solution layer, and finally the dispersion solvent molecules, the coating agent molecules, and the liquid repellent agent molecules are not left.

  Below, the structure of the metal nanoparticle dispersion liquid suitably used in the present invention will be described in more detail.

  Since the metal nanoparticle dispersion draws a fine planar pattern of the wiring layer with high accuracy, the average particle diameter of the metal nanoparticles ranges from 1 to 100 nm according to the target minimum line width and planar shape size. Select Preferably, the average particle size is selected in the range of 1-20 nm. By selecting the average particle diameter of the contained metal nanoparticles within the above range, application to a pattern with a fine line width is enabled by an ink jet printing apparatus.

  In order to prevent aggregation of metal nanoparticles in the dispersion, a coating layer made of a low molecule is provided on the surface of the metal nanoparticles and is dispersed in the liquid. That is, an oxide film is formed on the surface of the metal nanoparticles so that the coating layer on which the metal nanoparticle dispersion is laminated is heat-treated to cause fusion between the contained metal nanoparticles and the contact interface thereof. Use what is in a state that does not substantially exist.

  Specifically, the surface of the metal nanoparticle is composed of one or more compounds having a group containing nitrogen, oxygen, or sulfur atom as a group capable of coordinative bonding with the metal element contained in the metal nanoparticle. Covered. That is, the metal surface of the metal nanoparticle is uniformly formed by using one or more compounds having a group containing nitrogen, oxygen, or sulfur atom as a group capable of coordinately bonding with the metal element contained in the metal nanoparticle. For example, a dispersion of metal nanoparticles dispersed in one or more organic solvents is used while maintaining a state of being covered with, for example, an amine compound having one or more terminal amino groups.

  The role of this coating layer is to prevent aggregation of metal nanoparticles contained in the dispersion by keeping the metal surfaces in direct contact with each other until heat treatment is performed. It is to keep the cohesion resistance of the high. In addition, even when it is in contact with water or oxygen molecules in the atmosphere, such as when coating, the surface of the metal nanoparticles is already covered with a coating layer, leading to direct contact with water molecules and oxygen molecules. Therefore, it also has a function of suppressing the formation of a natural oxide film on the surface of the metal ultrafine particles due to moisture and oxygen molecules in the atmosphere.

  The compound used for the uniform coating of the surface of the metal nanoparticle uses a group having a lone pair on a nitrogen, oxygen, or sulfur atom when forming a coordinate bond with the metal element. . For example, an amino group is mentioned as a group containing a nitrogen atom. Examples of the group containing a sulfur atom include a sulfanyl group (—SH) and a sulfide type sulfanediyl group (—S—). Examples of the group containing an oxygen atom include a hydroxy group (—OH) and an ether type oxy group (—O—).

  A representative example of the compound having an amino group that can be used is an alkylamine. Such an alkylamine is preferably one that does not desorb in a normal storage environment, specifically in a range not reaching 40 ° C., in a state in which a coordinate bond is formed with the metal element, and has a boiling point. A range of 60 ° C. or higher, preferably 100 ° C. or higher, and more preferably 150 ° C. or higher is preferable. On the other hand, when the heat treatment of the conductive nanoparticle paste is performed, it is necessary that the conductive nanoparticle paste can be vaporized together with the dispersion solvent after leaving the surface of the metal nanoparticles. An alkylamine having a boiling point that does not exceed 300 ° C., usually 250 ° C. or lower is preferable. For example, as the alkylamine, those having an alkyl group selected in the range of C8 to C18 and having an amino group at the end of the alkyl chain are used. For example, alkylamines in the range of C8 to C18 have thermal stability, and the vapor pressure near room temperature is not so high. When stored at room temperature or the like, the content is maintained within a desired range. It is preferably used in terms of handling properties, such as being easy to control.

  In general, in forming such a coordination bond, the primary amine type is preferable because it shows higher binding ability, but secondary amine type and tertiary amine type compounds can also be used. is there. In addition, compounds in which two or more adjacent amino groups are involved in bonding, such as 1,2-diamine type and 1,3-diamine type, can also be used. In addition, a polyamine type compound having a relatively small molecular weight that can be dissolved in a dispersion solvent can be used. In some cases, a chain amine compound containing a polyoxyalkyleneamine type ether type oxy group (—O—) in the chain may be used. In addition to the terminal amino group, a hydrophilic terminal group such as a hydroxylamine having a hydroxyl group, such as ethanolamine, can also be used.

  Moreover, alkanethiol can be mentioned as a typical example of a compound having a sulfanyl group (—SH) that can be used. In addition, such alkanethiol is preferably in a state in which a coordinate bond is formed with a metal element and does not desorb in a normal storage environment, specifically, in a range not reaching 40 ° C., and has a boiling point. A range of 60 ° C. or higher, preferably 100 ° C. or higher, and more preferably 150 ° C. or higher is preferable. On the other hand, when heat-treating the coating film of the metal nanoparticle dispersion liquid, it is necessary to be able to evaporate together with the dispersion solvent after leaving the surface of the metal nanoparticle. At least alkanethiol having a boiling point not exceeding 300 ° C., usually 250 ° C. or less is preferable. For example, as the alkanethiol, C4-C20 is used as the alkyl group, and more preferably C8-C18 is selected, and an alkyl chain having a sulfanyl group (—SH) is used. For example, alkanethiols in the range of C8 to C18 have thermal stability, and the vapor pressure near room temperature is not so high. When stored at room temperature or the like, the content is maintained and controlled within a desired range. It is preferably used in terms of handling properties, such as being easy to do. In general, primary thiol type compounds are preferred because they exhibit higher binding ability, but secondary thiol type and tertiary thiol type compounds can also be used. In addition, those in which two or more sulfanyl groups (—SH) are involved in binding, such as 1,2-dithiol type, can also be used. In addition, a polythioether type compound having a relatively small molecular weight that can be dissolved in a dispersion solvent can be used.

  Moreover, alkanediol can be mentioned as a representative of the compound which has a hydroxyl group which can be utilized. Examples include glycols such as ethylene glycol, diethylene glycol, and polyethylene glycol. A polyether type compound having a relatively small molecular weight that can be dissolved in a dispersion solvent can also be used. In addition, such alkanediols are preferably those that do not desorb in a normal storage environment, specifically in a range that does not reach 40 ° C., in a state in which a coordinate bond is formed with the metal element. A range of 60 ° C. or higher, usually 100 ° C. or higher, and more preferably 150 ° C. or higher is preferable. On the other hand, when heat-treating the multilayer coating layer containing metal nanoparticles, it is necessary to be able to evaporate together with the dispersion solvent after leaving the surface of the metal nanoparticles. Alkanediols having a boiling point not exceeding 300 ° C., usually 250 ° C. or less, are preferred. For example, those involving two or more hydroxy groups, such as 1,2-diol type, can be used more suitably.

  The metal nanoparticles contained in the metal nanoparticle dispersion include one or more compounds containing the above-described nitrogen, oxygen, or sulfur atoms, and having a group that can be coordinated by a lone pair of electrons of these atoms. Are dispersed in a dispersion solvent in a state of having a surface coating layer. Such a surface coating layer has an appropriate coating ratio so that unnecessary excessive coating molecules do not exist within a range in which it can function to avoid direct contact between the surfaces of the metal nanoparticles during storage. select. That is, when heating at a low temperature by laser light irradiation, these coating layer molecules can be eluted and separated in the coexisting dispersion solvent, and the coating protective function is achieved. Select the coverage ratio within the achievable range. For example, with respect to 100 parts by mass of metal nanoparticles, one or more compounds having the above-described nitrogen, oxygen, or sulfur atom and having a group capable of coordinated bonding by a lone electron pair possessed by these atoms as a sum total Generally, it is preferable to select the coating ratio so as to contain 10 to 50 parts by mass, more preferably 20 to 50 parts by mass. In addition, with respect to 100 parts by mass of the metal nanoparticle, the surface of the metal nanoparticle includes a nitrogen atom, an oxygen atom, or a sulfur atom, and a group capable of coordinative bonding by a lone electron pair possessed by these atoms. The sum total of one or more compounds also depends on the average particle size of the metal nanoparticles. That is, when the average particle diameter of the metal nanoparticles becomes smaller, the total surface area of the nanoparticle surface per 100 parts by mass of the metal nanoparticles increases in inverse proportion to the average particle diameter. Need a higher ratio. In consideration of this point, when selecting the average particle diameter of the metal nanoparticles in the range of 1 to 20 nm, the sum of the coating molecules covering the surface with respect to 100 parts by mass of the metal nanoparticles is: It is preferable to select in the range of 20 to 50 parts by mass.

  The organic solvent used as a dispersion solvent contained in the metal nanoparticle dispersion liquid has a role of dispersing the metal nanoparticles provided with the above-described surface coating layer at room temperature. It functions as a solvent capable of eluting and releasing the coating layer molecules on the particle surface. At that time, a high-boiling liquid organic substance in which transpiration does not proceed remarkably is used in the elution stage of the coating layer molecules in the heated state by laser light irradiation. Accordingly, when heated to 100 ° C. or higher, preferably, 50 parts by mass or more of the compound having a group containing nitrogen, oxygen, or sulfur atoms covering the surface of the metal nanoparticles can be dissolved per 100 parts by mass of the dispersion solvent. In addition, one kind of organic solvent having high solubility or a mixed solvent composed of two or more kinds of liquid organic substances is used. In addition, when heated to 100 ° C. or higher, one kind of organic solvent capable of forming a compatible solution of any composition with respect to the compound having a group containing nitrogen, oxygen, or sulfur atoms that coats the surface of the metal nanoparticles, or It is more preferable to use a mixed solvent composed of two or more kinds of liquid organic substances, particularly those exhibiting high compatibility.

  Specifically, the coating layer molecule contains a nitrogen, oxygen, or sulfur atom, and is coordinated on the surface of the metal nanoparticle by using a group capable of coordinative bonding by a lone electron pair possessed by these atoms. is doing. At that time, utilizing the affinity for the remaining hydrocarbon chain and skeleton, the organic solvent contained in the dispersion solvent can maintain the dispersion state of the metal nanoparticles covered with the coating layer molecules, or achieve compatibility with each other. Demonstrate the function. Although the affinity of the coating layer molecule due to the coordinate bond to the surface of the metal nanoparticle is stronger than physical adsorption, it rapidly decreases with heating. On the other hand, as a result of the increase in the solubility characteristic of the organic solvent accompanying the increase in temperature, when the mixture is heated to a temperature higher than the equilibrium temperature, the desorption and elution of coating layer molecules are accelerated at an accelerated rate as the temperature increases. Eventually, almost all of the coating layer molecules on the surface of the metal nanoparticles are dissolved in the dispersion solvent present during heating, and substantially no coating layer molecules remain on the surface of the metal nanoparticles. Is achieved.

  Of course, since the elution process of the coating layer molecules from the surface of the metal nanoparticles and the reattachment process are in a thermal equilibrium relationship, the solubility of the coating layer molecules in the dispersion solvent during heating is sufficiently high. desirable. Even if the coating layer molecules are eluted into the dispersion solvent infiltrating the gaps between the stacked metal nanoparticles, the coating layer molecules are transferred from the inside of the coating layer to the outer edge through the narrow gaps. It takes more time to spread and flow out. In order to effectively suppress the reattachment of the coating layer molecules during the progress of the sintering between the metal nanoparticles, it is desirable to use the organic solvent exhibiting the high solubility described above.

  That is, the organic solvent used as a dispersion solvent shows affinity for the coating layer molecules on the surface of the metal nanoparticles, but the coating layer molecules on the surface of the metal nanoparticles easily elute into the organic solvent near room temperature. Although it does not occur, the solubility increases with heating, and when the coating layer molecules can be eluted into the organic solvent when heated to 100 ° C. or higher, those are used. For example, a compound that forms a coating layer on the surface of metal nanoparticles, for example, an amine compound such as an alkylamine contains a chain hydrocarbon group that has an affinity with the alkyl group portion, It is preferable to select a nonpolar solvent or a low polarity solvent instead of a solvent having such a high polarity that the solubility of the amine compound is too high and the coating layer on the surface of the metal nanoparticles disappears even at around room temperature. In addition, even at a temperature at which the low-temperature firing treatment is performed by laser light irradiation, the thermal stability is high enough to prevent thermal decomposition, and the boiling point is at least 80 ° C., preferably 150 ° C. or more and preferably not exceeding 300 ° C. Moreover, when forming a fine line, it is necessary to maintain a metal nanoparticle dispersion liquid in a desired liquid viscosity range in the coating process by the inkjet method. In consideration of the handling property, the non-polar solvent or the low-polar solvent having a high boiling point, which does not easily evaporate near room temperature, such as alkanes having 10 to 18 carbon atoms, such as tetradecane, etc. C8-12 primary alcohols such as 1-decanol are preferably used. However, the liquid viscosity of the dispersion solvent itself used is at least 10 mPa · s (20 ° C.) or less, preferably a solvent having a range of 0.2 to 3 mPa · s (20 ° C.) is selected. desirable.

  On the other hand, the metal nanoparticle dispersion liquid is used for drawing a fine pattern by applying an ink jet method which is a method of spraying and applying as fine droplets. Therefore, it is necessary to prepare the metal nanoparticle dispersion liquid having a liquid viscosity suitable for the drawing technique employed. Specifically, in order to use an inkjet method for drawing a fine wiring pattern, it is desirable to select the liquid viscosity of the metal nanoparticle dispersion in the range of 2 to 30 mPa · s (20 ° C.). At that time, the volume ratio of the dispersion solvent in the dispersion is more preferably selected in the range of 55 to 80% by volume. The liquid viscosity of the metal nanoparticle dispersion is determined depending on the average particle diameter of the metal nanoparticles to be used, the dispersion concentration, and the type of the dispersion solvent being used. The liquid viscosity can be adjusted.

  Specifically, the composition of the metal nanoparticle dispersion is such that when the volume ratio of the dispersion solvent in the dispersion is selected in the range of 55 to 80% by volume, the liquid viscosity is 2 to 30 mPa · It is preferable to be in the range of s (20 ° C.).

  For example, as a dispersion solvent, in addition to a nonpolar solvent or a low polarity solvent having a high boiling point as described above, the liquid viscosity is adjusted, and when heating by laser light irradiation is performed, it is useful for elution of coating layer molecules. In the vicinity of room temperature, a liquid organic substance having a relatively low polarity that exhibits a function of suppressing the separation of the coating layer molecules and a function of compensating for the separation can be added and blended. Such a low-polarity liquid organic substance added and blended can achieve uniform mixing with the main solvent component, and the boiling point of the liquid organic material should be as high as the main solvent component. desirable. For example, when the main solvent component is a primary alcohol having 8 to 12 carbon atoms, such as 1-decanol, branched diols such as 2-ethyl-1,3-hexanediol, When the main solvent component is an alkane having 10 to 18 carbon atoms, such as tetradecane, a dialkylamine having a branch such as bis-2-ethylhexylamine is supplementally added and blended. It can be used as a low-polar liquid organic material.

During the heat treatment, the coating layer molecules such as alkylamine coating the surface of the metal nanoparticles are eluted and separated from the dispersion solvent, and the coating layer that has suppressed the aggregation of the metal nanoparticles disappears. As a result, the metal nanoparticles are gradually fused and agglomerated by fusion, and finally a random chain is formed. At this time, the low-temperature sintering of the metal nanoparticles proceeds, the space between the metal nanoparticles decreases, the entire volume shrinks, and the random chains achieve close contact with each other. When the space between the metal nanoparticles decreases, the dispersion solvent that occupies this space maintains fluidity, so even if the space between the metal nanoparticles becomes a bottleneck, it is pushed out to the outside. The whole volume shrinkage proceeds. In this low-temperature firing process, the heat treatment temperature by laser light irradiation is selected within a temperature range that does not damage the substrate itself. Specifically, in the low-temperature firing process, the heat treatment temperature by laser light irradiation is usually 250 ° C. or lower, preferably 100 ° C. to 230 ° C., more preferably 130 ° C. to 200 ° C. . At that time, the coating layer molecules are eluted and separated in the above-mentioned dispersion solvent, and the obtained sintered metal nanoparticles have a smooth surface without surface irregularities reflecting non-uniform aggregation of metal nanoparticles. Show shape. In addition, the conductor layer is denser and has a very low resistance, for example, a volume resistivity of 10 × 10 ⁻⁶ Ω · cm or less. On the other hand, as the entire volume shrinks, the dispersion solvent to be pushed out and the coating layer molecules dissolved therein gradually evaporate while continuing the heating by laser light irradiation, and finally the metal nano-particles obtained. The amount of organic matter remaining in the sintered body of particles is limited.

  Specifically, the volume occupancy of the sintered body of metal nanoparticles in the conductor layer itself is high. As a result, in addition to the low volume resistivity of the sintered body of metal nanoparticles itself, the thermal conductivity of the entire conductor layer is also greatly improved due to the high volume occupancy of the metal body. .

  In the method according to the present invention, a conductor layer made of a sintered body of metal nanoparticles formed by the low-temperature firing process is used for forming a wiring layer on a substrate. Therefore, the metal species constituting the metal nanoparticles to be used are selected from metal species suitable for the wiring layer. For example, the metal nanoparticles dispersed in the metal nanoparticle dispersion liquid are selected from the group of metals consisting of gold, silver, platinum, palladium, nickel, titanium, nanoparticles composed of one kind of metal, A mixture of nanoparticles composed of two or more metals or a nanoparticle composed of an alloy of two or more metals selected from the group of the metals is preferred.

  In particular, when a copper plate formed of electrolytic copper or a substrate having a copper foil as a conductive layer is employed as the substrate, it is preferable to select silver nanoparticles as the metal nanoparticles.

  Moreover, when employ | adopting the board | substrate which coat | covers a polyimide layer as a board | substrate, it is preferable to select a silver nanoparticle as a metal nanoparticle.

  Hereinafter, the present invention will be described more specifically with reference to examples. Although these examples are examples of the best mode of the present invention, the present invention is not limited to these specific examples.

Example 1
Example 1 applies the method for forming a highly adhesive metal nanoparticle sintered body film according to the first aspect of the present invention, and comprises a metal nanoparticle sintered body film on a substrate coated with a polyimide layer. This is an example of producing a wiring layer.

  As the substrate, a substrate covered with a polyimide layer is adopted, and a liquid repellent coating layer is coated on the entire surface of the polyimide layer. This liquid repellent coating layer is in a state in which a liquid repellent: a fluorine-based surface treatment agent EGC-1720, 3M Novec (Sumitomo 3M Limited) is uniformly applied to a film thickness of about 10 nm.

  As a metal nanoparticle dispersion liquid, a dispersion layer N14 (tetradecane) formed by forming a coating molecular layer of dodecylamine (melting point: 28.3 ° C., boiling point: 248 ° C.) on the surface of silver nanoparticles having an average particle diameter D of 3 nm. Viscosity of 2.0 to 2.3 mPa · s (20 ° C.), melting point of 5.86 ° C., boiling point of 253.57 ° C., manufactured by Nikko Petrochemical Co., Ltd.). The silver nanoparticle dispersion contains 20 parts by mass of the coating molecule dodecylamine and 52 parts by mass of the dispersion solvent N14 per 100 parts by mass of the silver nanoparticles. The liquid viscosity of the silver nanoparticle dispersion is 10 mPa · s (20 ° C.).

  The silver nanoparticle dispersion liquid is applied at a coating liquid thickness of 3 μm on a substrate coated with the polyimide layer and coated with the liquid repellent coating layer to prepare a coating liquid layer of the silver nanoparticle dispersion liquid.

  The coating liquid layer of this silver nanoparticle dispersion is subjected to a preliminary drying treatment at 100 ° C. for 60 seconds.

From the surface of the silver nanoparticle dispersion liquid coating layer, an Nd / YAG laser beam having a wavelength λ ₁ = 1064 nm is irradiated in the vertical direction with an irradiation spot diameter D ₁ = 100 μm and an average laser beam intensity P ₁ = 250 W / mm ² ( Irradiation is performed from an incident angle of 0 °. Under the irradiation conditions, the apparent reflectance R _{1 -upper} = 3% on the surface of the silver nanoparticle dispersion coating liquid layer, the apparent transmittance T _1-upper = 74% on the silver nanoparticle dispersion coating liquid layer, Apparent reflectance R _1-lower = 1% at the interface of the polyimide layer / silver nanoparticle dispersion coating solution layer. Therefore, the apparent light absorptance A _1-upper = 23% in the silver nanoparticle dispersion coating liquid layer, and the ratio of light penetrating into the polyimide layer (effective transmittance) T _1-lower = 73%. Yes.

As a result, when the irradiation time t ₁ = 25 ms has passed (P ₁ · t ₁ ≧ 6250 ms · W / mm ² ), the temperature T _{1 -bottom} = 120 at the interface of the polyimide layer / silver nanoparticle dispersion coating liquid layer The temperature of the surface of the silver nanoparticle dispersion coating liquid layer T _{1 -top} = 90 ° C.

The liquid repellent: fluorine-based surface treatment agent EGC-1720 (boiling point: 61 ° C.) used for the liquid repellent coating layer for coating the polyimide layer surface itself does not absorb the laser beam having the wavelength λ ₁ = 1064 nm. On the other hand, at a temperature T _1-bottom = 110 ° C. at the polyimide layer / silver nanoparticle dispersion coating liquid layer interface, the liquid repellent: fluorine-based surface treatment agent EGC-1720 is a dispersion solvent of silver nanoparticle dispersion: N14 Dissolve in As a result, the liquid repellent coating layer existing at the interface between the silver nanoparticle dispersion coating liquid layer and the polyimide layer was selectively applied to the portion that was in contact with the silver nanoparticle dispersion coating liquid layer and irradiated with the laser beam. Removal is done.

At that time, the polyimide layer itself exhibits light absorption for laser light having a wavelength of λ ₁ = 1064 nm, and undergoes photoactivation due to this light absorption. Specifically, modification is performed with photoactivation in the polyimide layer. For example, a partial imide ring opening reaction proceeds in the laser exposure region. By this partial imide ring opening, for example, a —COOH-type functional group derived from an imide ring and a —CO—NH— bond are generated. By the modification of the polyimide layer, for example, a -COOH type functional group or a -CO-NH- bond part generated on the surface has a function of forming a bond with a silver atom on the surface of the silver nanoparticle. It has. Therefore, by the modification of the polyimide layer, the structure such as a —COOH type functional group and —CO—NH— bond produced on the surface of the polyimide layer interacts with the silver nanoparticles, Demonstrates the ability to improve adhesion.

Subsequently, from the surface of the silver nanoparticle dispersion liquid coating layer, a laser beam having a wavelength λ ₂ = 1064 nm is irradiated in the vertical direction (incident angle) with an irradiation spot diameter D ₂ = 100 μm and an average laser beam intensity P ₂ = 50 W / mm ^2. Irradiate from 0 °. Under this irradiation condition, the apparent reflectance R _2-upper at the surface of the silver nanoparticle dispersion coating liquid layer at the start of irradiation R _{2 -upper} = 3%, the apparent transmittance T _{2-upper of the} silver nanoparticle dispersion coating liquid layer = 74%, Apparent reflectance R _2-lower = 1% at the interface of the polyimide layer / silver nanoparticle dispersion coating solution layer. Therefore, the apparent light absorption rate A _2-upper in the silver nanoparticle dispersion coating liquid layer is 23%, and the ratio of light penetrating into the polyimide layer (effective transmittance) is T _2-lower = 73%. Yes.

On the surface of silver nanoparticles having an average particle diameter of 3 nm, localized plasmon absorption occurs by irradiation with laser light having a wavelength λ ₂ = 1064 nm. At that time, the coating molecule dodecylamine covering the surface of the silver nanoparticle is excited by the localized plasmon and is in a vibrationally excited state. As a result, the release of the coating molecule dodecylamine covering the surface of the silver nanoparticles is promoted.

At that time, when the irradiation time t ₂ = 10 ms has elapsed (P ₂ · t ₂ ≧ 500 ms · W / mm ² ), the temperature T _2-bottom = 130 at the interface of the polyimide layer / silver nanoparticle dispersion liquid coating solution layer. The surface temperature of the silver nanoparticle dispersion coating solution layer T _{2 -top} = 110 ° C.
Therefore, at the temperature T _{2 -bottom} = 130 ° C. at the polyimide layer / silver nanoparticle dispersion coating liquid layer interface, the _release of the coating molecule dodecylamine in the vibrationally excited state is promoted, resulting in removal of the surface coating layer. The modified silver nanoparticles adhere to the surface of the modified polyimide layer. Furthermore, the silver nanoparticles are produced by chemical adsorption through the interaction between the silver nanoparticles and the structure such as —COOH type functional groups and —CO—NH— bonds produced on the surface. Indicates high adhesion. A two-dimensional layer of silver nanoparticles fixed with high adhesion is formed on the surface of the modified polyimide layer. The fixed two-dimensional layer of silver nanoparticles is used as a nucleation layer, and silver nanoparticles from which the surface coating layer has been removed are stacked on the upper surface.

When a two-dimensional layer of silver nanoparticles adhering to the surface of the modified polyimide layer is formed, the apparent reflectance at the polyimide layer / silver nanoparticle dispersion liquid coating layer interface is the original R _{2. Increase} from _-lower = 1% to R _{2-metal-layer} = 95%. As a result, the ratio of light penetrating into the polyimide layer (effective transmittance) is reduced from the original T _2-lower = 73% to T _{2-metal-layer} = 4%.

When the irradiation time t ′ ₂ = 30 ms has elapsed and the silver nanoparticles are laminated on the surface of the modified polyimide layer, the temperature of the silver nanoparticle lamination portion is T ′ _2-bottom = The temperature of the surface of the silver nanoparticle dispersion liquid coating solution layer is 160 ° C., and T ′ _{2 -top} = 150 ° C. Therefore, part of the fusion of the laminated silver nanoparticles proceeds on the surface of the modified polyimide layer. On the surface of the coating liquid layer, evaporation of the coating molecule dodecylamine having a boiling point of 248 ° C. and the dispersion solvent N14 having a boiling point of 253.57 ° C. rapidly proceeds.

Thereafter, a laser beam having a wavelength λ ₃ = 1064 nm is irradiated from the surface of the coating liquid layer from the vertical direction (incident angle 0 °) with an irradiation spot diameter D ₃ = 100 μm and an average laser beam intensity P ₃ = 50 W / mm ^2. To do. Under this irradiation condition, the apparent reflectance R _3-upper at the surface of the coating liquid layer at the start of irradiation R _{3 -upper} = 3%, the apparent transmittance T ₃ -upper at the coating liquid layer (dispersion liquid layer) = 90%, silver Apparent reflectance R _{3-metal-layer} = 95% at the interface between the layer of nanoparticles and the coating solution layer. Therefore, the apparent light absorption rate A _3-upper = 7% in the coating liquid layer, and the ratio of light penetrating into the silver nanoparticle stack (effective light absorption rate) A _{3-metal-layer} = 10%. ing.

At that time, when the irradiation time t ₃ = 5 seconds passed (P ₃ · t ₃ ≧ 250 ms · W / mm ² ), the temperature T _{3 -bottom} = 180 ° C. at the interface between the silver nanoparticle laminate / coating liquid layer The surface temperature of the coating solution layer is T _3-top = 170 ° C. Therefore, fusion and low-temperature sintering of the laminated silver nanoparticles rapidly progress on the surface of the modified polyimide layer. In addition, on the surface of the coating liquid layer, the transpiration of the remaining coating agent molecule dodecylamine having a boiling point of 248 ° C. and the dispersion solvent N14 having a boiling point of 253.57 ° C. is accelerated. Finally, when the irradiation time t ′ ₃ = 30 seconds (P ₃ · t ′ ₃ ≧ 1500 ms · W / mm ² ), the laser exposure region is sintered at a low temperature, silver nanoparticle sintered A thin film layer of the body is formed. The average film thickness of the thin film layer of the formed silver nanoparticle sintered body is about 0.5 μm.

  The average film thickness of about 0.5 μm of the thin film layer of the silver nanoparticle sintered body corresponds to about 1/6 with respect to the initial coating liquid thickness of 3 μm. The volume ratio of the silver nanoparticles in the silver nanoparticle dispersion is about 12% by volume. When the silver nanoparticles in the coating liquid thickness of 3 μm are converted into bulk silver, the film thickness corresponds to 0.35 μm. . Therefore, dense sintering is achieved in the thin film layer of the produced silver nanoparticle sintered body.

  That is, the process of forming the thin film layer of the silver nanoparticle sintered body is composed of the following five steps.

(Step A-1) Step of producing silver nanoparticle dispersion liquid coating layer:
Liquid repellent: EGC-1720 coated with a liquid repellent coating layer having an average film thickness of 10 nm and coated with a polyimide layer, a silver nanoparticle dispersion liquid is applied in a predetermined planar shape with a coating liquid thickness of 3 μm. Apply to prepare a coating solution layer.

(Step A-1 ′) Predrying treatment step of coating solution layer:
The silver nanoparticle dispersion liquid coating layer is subjected to a preliminary drying treatment at 100 ° C. for 60 seconds.

(Step A-2) First laser light irradiation step:
From the surface of the silver nanoparticle dispersion coating liquid layer, a laser beam having a wavelength of λ ₁ = 1064 nm is irradiated in a vertical direction (incident angle 0 ° with an irradiation spot diameter D ₁ = 100 μm, an average laser beam intensity P ₁ = 250 W / mm ² . ). Under this condition, irradiation with a laser beam with an irradiation time t ₁ = 20 seconds selectively removes the liquid repellent coating layer composed of the liquid repellent: EGC-1720 in the region in contact with the coating liquid layer irradiated with the laser beam. Is done. In addition, the surface of the polyimide layer that has been laser-exposed is modified in the region in contact with the coating liquid layer.

(Step A-3) Second laser light irradiation step:
Subsequently, from the surface of the silver nanoparticle dispersion coating liquid layer, a laser beam having a wavelength λ ₂ = 1064 nm is irradiated in the vertical direction (incident with an irradiation spot diameter D ₂ = 100 μm, an average laser beam intensity P ₂ = 50 W / mm ^2. Irradiate from an angle of 0 °. Under this condition, the coating material molecule layer composed of the coating agent molecule dodecylamine was removed on the surface of the modified polyimide layer by performing laser irradiation for a total irradiation time t ′ ₂ = 30 seconds. A stack of nanoparticles is formed. At this stage, the silver nanoparticles adhering to the modified surface of the polyimide layer interact with the structure such as a —COOH type functional group and —CO—NH— bond produced by the modification. Thus, high adhesion is exhibited on the surface of the modified polyimide layer by chemical adsorption. With the silver nanoparticles adhering to the modified polyimide layer surface serving as a nucleus, lamination of the silver nanoparticles from which the coating agent molecular layer has been removed proceeds. At that time, a part of the fusion of the laminated silver nanoparticles proceeds. In parallel, evaporation of the coating molecule dodecylamine, which is removed and dissolved in the dispersion solvent, and the dispersion solvent N14 proceed on the surface of the coating liquid layer.

(Step A-4) Third laser light irradiation step:
Finally, from the surface of the coating liquid layer, a laser beam having a wavelength λ ₃ = 1064 nm is irradiated in the vertical direction (incident angle 0 °) with an irradiation spot diameter D ₃ = 100 μm and an average laser beam intensity P ₃ = 50 W / mm ² . Irradiate from. Under these conditions, laser light irradiation for a total irradiation time t ′ ₃ = 30 seconds is performed, and fusion and low-temperature sintering of the laminated silver nanoparticles are completed on the surface of the modified polyimide layer. The In parallel, on the surface of the coating liquid layer, the evaporation of the dispersion solvent N14 and the coating molecule molecule dodecylamine dissolved in the dispersion solvent is accelerated, and a thin film layer of a silver nanoparticle sintered body is formed. Is completed.

(Comparative Example 1)
In Comparative Example 1, the thickness of the coating liquid layer of the metal nanoparticle dispersion applied on the substrate coated with the polyimide layer is three times that of Example 1, and the laser reaches the polyimide layer surface when irradiated with laser light. This is an example of selecting a condition that makes the light intensity equal to that in Example 1 and forming a metal nanoparticle sintered body film.

  As the substrate, a substrate covered with a polyimide layer is adopted, and a liquid repellent coating layer is coated on the entire surface of the polyimide layer. This liquid repellent coating layer is in a state where liquid repellent: fluorine-based surface treatment agent EGC-1720 is uniformly applied to a thickness of about 10 nm.

  As a metal nanoparticle dispersion liquid, a dispersion layer N14 (tetradecane) formed by forming a coating molecular layer of dodecylamine (melting point: 28.3 ° C., boiling point: 248 ° C.) on the surface of silver nanoparticles having an average particle diameter D of 3 nm. Viscosity of 2.0 to 2.3 mPa · s (20 ° C.), melting point of 5.86 ° C., boiling point of 253.57 ° C., manufactured by Nikko Petrochemical Co., Ltd.). The silver nanoparticle dispersion contains 20 parts by mass of the coating molecule dodecylamine and 52 parts by mass of the dispersion solvent N14 per 100 parts by mass of the silver nanoparticles. The liquid viscosity of the silver nanoparticle dispersion is 10 mPa · s (20 ° C.).

  The silver nanoparticle dispersion liquid is applied with a coating liquid thickness of 9 μm onto a substrate coated with the polyimide layer and coated with the liquid repellent coating layer, thereby preparing a coating liquid layer of the silver nanoparticle dispersion liquid.

  The coating liquid layer of this silver nanoparticle dispersion is subjected to a preliminary drying treatment at 100 ° C. for 60 seconds.

Laser light having a wavelength λ ₁ = 1064 nm is irradiated from the surface of the silver nanoparticle dispersion liquid coating layer from the vertical direction (incident angle 0 °) with an irradiation spot diameter D ₁ = 100 μm. At that time, the light transmittance of the coating solution layer of the silver nanoparticle dispersion decreases approximately in proportion to exp (−A · d) with respect to the thickness d of the coating solution layer. Therefore, the apparent transmittance of the silver nanoparticle dispersion coating liquid layer is reduced to T _1-upper = 40% under the condition of Comparative Example 1 as compared to the value of Example 1, T _1-upper = 74%. To do. Therefore, under the condition of the coating liquid thickness of 9 μm, the apparent reflectance R _1-upper = 3% on the surface of the silver nanoparticle dispersion liquid coating liquid layer, and the apparent transmittance T _{1− of the} silver nanoparticle dispersion liquid coating liquid layer _upper = 40%, apparent reflectance R _1−lower = 1% at the interface of the polyimide layer / silver nanoparticle dispersion coating solution layer.

The intensity of the laser beam applied to the polyimide layer / silver nanoparticle dispersion coating liquid layer interface is made substantially equal to the laser beam intensity in Example 1. Therefore, the average laser light intensity irradiated on the surface of the coating liquid layer is P ₁ = 500 W / mm ^{2 under} the condition of Comparative Example 1 as compared to the value P ₁ = 250 W / mm ^{2 in} Example 1. It is greatly increased.

  The heating of the polyimide layer surface depends on the intensity of the laser beam applied to the polyimide layer / silver nanoparticle dispersion coating solution layer interface. Under the above irradiation conditions, the intensity of the laser beam applied to the interface is the same, so the temperature of the polyimide layer surface is also substantially the same. On the other hand, the heating of the coating liquid layer surface depends on the average laser light intensity irradiated on the surface of the coating liquid layer. Under the above irradiation conditions, the average laser light intensity irradiated to the surface of the coating liquid layer is increased about twice, so that the temperature of the surface of the coating liquid layer is significantly increased.

As a result, when the irradiation time t ₁ = 25 seconds passed (P ₁ · t ₁ ≧ 12,500 ms · W / mm ² ), the temperature at the interface of the polyimide layer / silver nanoparticle dispersion coating liquid layer was T _{At 1-bottom} = 150 ° C., the temperature of the surface of the silver nanoparticle dispersion liquid coating solution reaches T _1-top = 140 ° C.

The liquid repellent agent: EGC-1720 itself used for the liquid repellent coating layer for coating the polyimide layer surface does not absorb the laser beam having the wavelength λ ₁ = 1064 nm. On the other hand, at a temperature T ₁ -bottom = 150 ° C. at the polyimide layer / silver nanoparticle dispersion coating liquid layer interface, the liquid repellent: EGC-1720 dissolves in the dispersion solvent: N14 of the silver nanoparticle dispersion. As a result, the liquid repellent coating layer existing at the interface between the silver nanoparticle dispersion coating liquid layer and the polyimide layer was selectively applied to the portion that was in contact with the silver nanoparticle dispersion coating liquid layer and irradiated with the laser beam. Removal is done.

At that time, the intensity of the laser beam applied to the interface of the polyimide layer / silver nanoparticle dispersion coating solution layer is made substantially equal to the laser beam intensity in Example 1. The polyimide layer itself exhibits light absorption for laser light having a wavelength of λ ₁ = 1064 nm and undergoes photoactivation due to this light absorption. Specifically, in Comparative Example 1, as in Example 1, the modification is performed with the photoactivation in the polyimide layer.

Subsequently, a laser beam having a wavelength λ ₂ = 1064 nm is irradiated from the surface of the silver nanoparticle dispersion coating liquid layer from the vertical direction (incident angle 0 °) with an irradiation spot diameter D ₂ = 100 μm. Even under this irradiation condition, the light transmittance of the coating solution layer of silver nanoparticle dispersion decreases approximately in proportion to exp (−A · d) with respect to the thickness d of the coating solution layer. Therefore, at the start of irradiation, the apparent transmittance of the silver nanoparticle dispersion liquid coating layer is the value of Example 1, T _2-upper = 74%, whereas in the condition of Comparative Example 1, T _2-upper = Reduce to 40%. Therefore, under the condition of the coating liquid thickness of 9 μm, the apparent reflectance R _2-upper = 3% on the surface of the silver nanoparticle dispersion liquid coating liquid layer, and the apparent transmittance T _{2− of the} silver nanoparticle dispersion liquid coating liquid layer. _upper = 40%, apparent reflectance R _2-lower = 1% at the interface of the polyimide layer / silver nanoparticle dispersion coating solution layer. Therefore, the apparent light absorption rate A _2-upper in the silver nanoparticle dispersion coating liquid layer is 57%, and the ratio of light penetrating into the polyimide layer (effective transmittance) is T _2-lower = 39%. Yes.

The intensity of the laser beam applied to the polyimide layer / silver nanoparticle dispersion coating liquid layer interface is made substantially equal to the laser beam intensity in Example 1. Therefore, the average laser light intensity irradiated on the surface of the coating liquid layer is P ₂ = 100 W / mm ^{2 under} the condition of Comparative Example 1 as compared to the value P ₂ = 50 W / mm ^{2 in} Example 1. It is greatly increased.

On the surface of silver nanoparticles having an average particle diameter of 3 nm, localized plasmon absorption occurs by irradiation with laser light having a wavelength λ ₂ = 1064 nm. At that time, the coating molecule dodecylamine covering the surface of the silver nanoparticle is excited by the localized plasmon and is in a vibrationally excited state. As a result, the release of the coating molecule dodecylamine covering the surface of the silver nanoparticles is promoted.

At that time, under the irradiation conditions of Comparative Example 1, when the irradiation time t ₂ = 5 seconds passed (P ₂ · t ₂ ≧ 500 ms · W / mm ² ), the polyimide layer / silver nanoparticle dispersion coating liquid layer temperature at the _{interface, T 2-bottom = 160 ℃} , the temperature of the surface of the silver nanoparticle dispersion coating liquid layer reaches the T _2-top = 160 ℃.

Therefore, at the temperature T _{2 -bottom} = 160 ° C. at the polyimide layer / silver nanoparticle dispersion coating liquid layer interface, the _release of the coating molecule dodecylamine in the vibrationally excited state is promoted, resulting in removal of the surface coating layer. The modified silver nanoparticles adhere to the surface of the modified polyimide layer.

Further, at a temperature T _2-top = 160 ° C. on the surface of the coating solution layer, the _release of the coating molecule dodecylamine in a vibrationally excited state is promoted, resulting in the removal of the surface coating layer of the silver nanoparticles. The silver nanoparticles from which the surface coating layer has been removed are fused together to form an aggregate. That is, in the vicinity of the surface of the silver nanoparticle dispersion coating liquid layer, silver nanoparticles are fused to each other to form a layer forming an aggregate. Using the silver nanoparticle aggregate layer as a core, the silver nanoparticle aggregates produced in the silver nanoparticle dispersion liquid coating layer are connected at a sparse density.

At this time, the silver nanoparticle aggregate layer blocks laser light having a wavelength of λ ₂ = 1064 nm and inhibits the laser light from entering the silver nanoparticle dispersion coating liquid layer. As a result, the dissociation process of the coating molecule dodecylamine, which is promoted by the vibration excitation of the coating molecule dodecylamine, caused by the irradiation with the laser beam having the wavelength λ ₂ = 1064 nm, in the coating layer of the silver nanoparticle dispersion liquid is Be inhibited. That is, the silver nanoparticle dispersion liquid coating liquid layer is in a state where silver nanoparticles holding the coating agent molecule layer made of the coating agent molecule dodecylamine remain in a considerable ratio.

  On the other hand, on the surface of the coating liquid layer, the transpiration of the dispersion solvent N14 and the coating agent molecule dodecylamine dissolved in the dispersion solvent rapidly proceeds.

  As a result, when the dispersion solvent evaporates, a layer structure in which agglomerates of silver nanoparticles are connected at a sparse density is formed on the surface of the coating liquid layer, and a coating molecular layer is formed in the lower layer portion. There is a state in which there is a region where silver nanoparticles holding s are contained in a considerable ratio.

Finally, from the surface of the coating liquid layer, a laser beam having a wavelength λ ₃ = 1064 nm is irradiated in the vertical direction (incident angle 0 °) with an irradiation spot diameter D ₃ = 100 μm and an average laser beam intensity P ₃ = 100 W / mm ² . Irradiate from. In Comparative Example 1, under this irradiation condition, the apparent reflectance R _3-upper = 3% on the surface of the coating liquid layer at the start of irradiation, the apparent transmittance T _3-upper = 10% on the surface of the coating liquid layer, silver Apparent reflectance R _{3-metal-layer} = 95% at the interface between the layer of nanoparticles and the coating solution layer. Accordingly, the apparent light absorption rate A _3-upper = 85% in the coating liquid layer, the ratio of light penetrating into the silver nanoparticle aggregate layer (effective light absorption rate) A _{3-metal-layer} = 85% It has become.

  Under this condition, low-temperature sintering proceeds in the layer structure portion formed by the aggregation of silver nanoparticles connected on the surface of the coating solution layer at a sparse density. However, the lower layer portion is a region where silver nanoparticles holding the coating agent molecular layer are contained in a considerable ratio, and low temperature sintering does not proceed in the lower layer portion. Of course, the adhesiveness to the surface of the modified polyimide layer is poor.

(Example 2)
Example 2 applies the method for forming a highly adhesive metal nanoparticle sintered body film according to the second aspect of the present invention to produce a wiring layer made of a metal nanoparticle sintered body film on a copper substrate. This is an example.

  As the substrate, a substrate having an electrolytic copper conductor layer is employed, and a liquid repellent coating layer is coated on the entire surface of the electrolytic copper conductor layer. This liquid repellent coating layer is in a state where liquid repellent: fluorine-based surface treatment agent EGC-1720 is uniformly applied to a thickness of about 10 nm.

  As a metal nanoparticle dispersion liquid, a dispersion layer N14 (tetradecane) formed by forming a coating molecular layer of dodecylamine (melting point: 28.3 ° C., boiling point: 248 ° C.) on the surface of silver nanoparticles having an average particle diameter D of 3 nm. Viscosity of 2.0 to 2.3 mPa · s (20 ° C.), melting point of 5.86 ° C., boiling point of 253.57 ° C., manufactured by Nikko Petrochemical Co., Ltd.). The silver nanoparticle dispersion contains 20 parts by mass of the coating molecule dodecylamine and 52 parts by mass of the dispersion solvent N14 per 100 parts by mass of the silver nanoparticles. The liquid viscosity of the silver nanoparticle dispersion is 10 mPa · s (20 ° C.).

  The silver nanoparticle dispersion liquid is applied at a coating liquid thickness of 3 μm on the surface of the electrolytic copper conductor layer coated with the liquid repellent coating layer to produce a silver nanoparticle dispersion liquid coating liquid layer.

  The coating liquid layer of this silver nanoparticle dispersion is subjected to a preliminary drying treatment at 100 ° C. for 60 seconds.

From the surface of the silver nanoparticle dispersion liquid coating layer, a laser beam having a wavelength λ ₁ = 1064 nm is irradiated in the vertical direction (incident with an irradiation spot diameter D ₁ = 100 μm, an average laser beam intensity P ₁ = 13,000 W / mm ^2. Irradiate from an angle of 0 °. Under the irradiation conditions, the apparent reflectance R _{1 -upper} = 3% on the surface of the silver nanoparticle dispersion coating liquid layer, the apparent transmittance T _1-upper = 74% on the silver nanoparticle dispersion coating liquid layer, Apparent reflectance R _1-lower = 60% at the interface between the electrolytic copper conductor layer / silver nanoparticle dispersion coating solution layer. Therefore, the apparent light absorption rate A _1-upper in the silver nanoparticle dispersion coating liquid layer is 23%, and the ratio of light penetrating into the conductor layer of electrolytic copper (effective absorption rate) A _1-lower = 29 %.

As a result, when the irradiation time t ₁ = 3 seconds has passed (P ₁ · t ₁ ≧ 39,000 ms · W / mm ² ), at the interface between the electrolytic copper conductor layer / silver nanoparticle dispersion coating liquid layer The temperature T _1-bottom = 140 ° C., and the temperature T _1-top = 120 ° C. of the surface of the silver nanoparticle dispersion coating liquid layer is obtained.

The liquid repellent: EGC-172 itself used for the liquid repellent coating layer for coating the surface of the electrolytic copper conductor layer does not absorb the laser beam having the wavelength λ ₁ = 1064 nm. On the other hand, at a temperature T ₁ -bottom = 140 ° C. at the interface between the electrolytic copper conductor layer / coating liquid layer, the liquid repellent: EGC-1720 dissolves in the dispersion solvent: N14 of the silver nanoparticle dispersion. As a result, the liquid repellent coating layer that was present at the interface between the silver nanoparticle dispersion coating solution layer and the electrolytic copper conductor layer in the portion that was in contact with the silver nanoparticle dispersion coating solution layer and irradiated with the laser beam. Is selectively removed.

Subsequently, from the surface of the silver nanoparticle dispersion liquid coating layer, a laser beam having a wavelength λ ₂ = 1064 nm is irradiated in a vertical direction (with an irradiation spot diameter D ₂ = 100 μm, an average laser beam intensity P ₂ = 1,500 W / mm ² ). Irradiation is performed from an incident angle of 0 °. Under this irradiation condition, the apparent reflectance R _2-upper at the surface of the silver nanoparticle dispersion coating liquid layer at the start of irradiation R _{2 -upper} = 3%, the apparent transmittance T _{2-upper of the} silver nanoparticle dispersion coating liquid layer = Apparent reflectance R2 _-lower = 60% at the interface between the electrolytic copper conductor layer / silver nanoparticle dispersion liquid coating liquid layer. Accordingly, the apparent light absorption rate A _{2 -upper} in the silver nanoparticle dispersion coating liquid layer is 23%, and the ratio of light penetrating into the electrolytic copper conductor layer (effective light absorption rate) A _{2 -lower} = 29%.

On the surface of silver nanoparticles having an average particle diameter of 3 nm, localized plasmon absorption occurs by irradiation with laser light having a wavelength λ ₂ = 1064 nm. At that time, the coating molecule dodecylamine covering the surface of the silver nanoparticle is excited by the localized plasmon and is in a vibrationally excited state. As a result, the release of the coating molecule dodecylamine covering the surface of the silver nanoparticles is promoted.

At that time, at the time when the irradiation time t ₂ = 1 second has passed (P ₂ · t ₂ ≧ 1,500 ms · W / mm ² ), at the interface of the electrolytic copper conductor layer / silver nanoparticle dispersion coating liquid layer The temperature T _{2 -bottom} = 160 ° C. and the temperature T _{2 -top} = 140 ° C. of the surface of the silver nanoparticle dispersion liquid coating solution layer are obtained.

Therefore, at the temperature T _{2 -bottom} = 160 ° C. at the interface between the electrolytic copper conductor layer / silver nanoparticle dispersion coating solution layer, the release of the coating molecule dodecylamine in the vibrationally excited state is promoted. The silver nanoparticles from which the coating layer has been removed adhere to the surface of the electrolytic copper conductor layer. Furthermore, when interdiffusion progresses between electrolytic copper and silver nanoparticles, an alloying region is formed, and high adhesion is exhibited. A two-dimensional layer of attached silver nanoparticles is formed on the surface of the electrolytic copper conductor layer. The two-dimensional layer of adhered silver nanoparticles is used as a nucleation layer, and silver nanoparticles from which the surface coating layer has been removed are stacked on the upper surface.

When a two-dimensional layer of silver nanoparticles adhered to the surface of the electrolytic copper conductor layer is formed, the apparent reflectance at the interface between the electrolytic copper conductor layer / silver nanoparticle dispersion coating liquid layer is It increases from the original R _2-lower = 60% to R _{2-metal-layer} = 95%. As a result, the ratio of light penetrating into the electrolytic copper conductor layer (effective light absorption rate) decreases from A _{2 -lower} = 29% to A _{2 -metal-layer} = 5%.

At the stage where the irradiation time t ′ ₂ = 3 seconds has passed (P ₂ · t ′ ₂ ≧ 4,500 ms · W / mm ² ) and the silver nanoparticles were laminated on the surface of the electrolytic copper conductor layer. The temperature of the laminated part of the silver nanoparticles is T ′ _2-bottom = 180 ° C., and the temperature of the surface of the silver nanoparticle dispersion liquid coating layer is T ′ _2-top = 170 ° C. Therefore, a part of the fusion of the laminated silver nanoparticles proceeds on the surface of the electrolytic copper conductor layer. On the surface of the coating liquid layer, evaporation of the coating molecule dodecylamine having a boiling point of 248 ° C. and the dispersion solvent N14 having a boiling point of 253.57 ° C. rapidly proceeds.

Thereafter, from the surface of the coating liquid layer, a laser beam having a wavelength λ ₃ = 1064 nm is irradiated in the vertical direction (incident angle 0 °) with an irradiation spot diameter D ₃ = 100 μm and an average laser beam intensity P ₃ = 1,500 W / mm ² . Irradiate from. Under this irradiation condition, the apparent reflectance R _3-upper at the surface of the coating liquid layer at the start of irradiation R _{3 -upper} = 3%, the apparent transmittance T ₃ -upper at the coating liquid layer (dispersion liquid layer) = 90%, silver Apparent reflectance R _{3-metal-layer} = 95% at the interface between the layer of nanoparticles and the coating solution layer. Therefore, the apparent light absorption rate A _3-upper = 7% in the coating liquid layer, and the ratio of light penetrating into the silver nanoparticle stack (effective light absorption rate) A _{3-metal-layer} = 4%. ing.

At that time, when the irradiation time t ₃ = 1 second has passed (P ₃ · t ₃ ≧ 1,500 ms · W / mm ² ), the temperature T ₃ -bottom at the interface of the silver nanoparticle stacking / coating liquid layer = 190 ° C., surface temperature T _3-top = 180 ° C. of the coating solution layer. Therefore, fusion and low-temperature sintering of the laminated silver nanoparticles proceed rapidly on the surface of the electrolytic copper conductor layer. In addition, on the surface of the coating liquid layer, the transpiration of the remaining coating agent molecule dodecylamine having a boiling point of 248 ° C. and the dispersion solvent N14 having a boiling point of 253.57 ° C. is accelerated. Finally, when the irradiation time t ′ ₃ = 3 seconds (P ₃ · t ′ ₃ ≧ 4,500 ms · W / mm ² ), the laser-exposed region has low-temperature sintered silver nanoparticles. A thin film layer of a sintered body is formed. The average film thickness of the thin film layer of the formed silver nanoparticle sintered body is about 0.5 μm.

  The average film thickness of about 0.5 μm of the thin film layer of the silver nanoparticle sintered body corresponds to about 1/6 with respect to the initial coating liquid thickness of 3 μm. The volume ratio of the silver nanoparticles in the silver nanoparticle dispersion is about 12% by volume. When the silver nanoparticles in the coating liquid thickness of 3 μm are converted into bulk silver, the film thickness corresponds to 0.35 μm. . Therefore, dense sintering is achieved in the thin film layer of the produced silver nanoparticle sintered body.

In addition, since the temperature at the interface between the electrolytic copper conductor layer / silver nanoparticles stack is substantially T _{3 -bottom} = 190 ° C., mutual diffusion between the electrolytic copper and the silver nanoparticles is further increased. As a result, an alloying region is formed on the entire interface, and high adhesion is exhibited.

  That is, the process of forming the thin film layer of the silver nanoparticle sintered body is composed of the following five steps.

(Step B-1) Step of producing silver nanoparticle dispersion liquid coating layer:
Liquid repellent: A silver nanoparticle dispersion liquid is applied in a predetermined planar shape onto a substrate having an electrolytic copper conductor layer coated with a liquid repellent coating layer having an average film thickness of 10 nm made of EGC-1720. Coating is performed at 3 μm to prepare a coating solution layer.

(Step B-1 ′) Preliminary drying treatment step of coating solution layer:
The silver nanoparticle dispersion liquid coating layer is subjected to a preliminary drying treatment at 100 ° C. for 60 seconds. (Step B-2) First laser light irradiation step:
From the surface of the silver nanoparticle dispersion coating liquid layer, a laser beam having a wavelength λ ₁ = 1064 nm is irradiated in a vertical direction (incident angle) with an irradiation spot diameter D ₁ = 100 μm and an average laser beam intensity P ₁ = 13,000 W / mm ^2. Irradiate from 0 °. Under this condition, laser light irradiation with an irradiation time t ₁ = 3 seconds selectively removes the liquid repellent coating layer composed of the liquid repellent: EGC-1720 in the region in contact with the coating liquid layer irradiated with the laser light. Is done.

(Step B-3) Second laser light irradiation step:
Subsequently, from the surface of the silver nanoparticle dispersion coating liquid layer, a laser beam having a wavelength λ ₂ = 1064 nm is irradiated in a vertical direction with an irradiation spot diameter D ₂ = 100 μm, an average laser beam intensity P ₂ = 1,500 W / mm ^2. Irradiate from (incident angle 0 °). Under this condition, a laser beam irradiation with a total irradiation time t ′ ₂ = 3 seconds was performed to remove the coating molecule layer composed of the coating molecule dodecylamine on the surface of the electrolytic copper conductor layer. A stack of nanoparticles is formed. At this stage, the silver nanoparticles adhering to the surface of the electrolytic copper conductor layer cause local interdiffusion with the electrolytic copper in contact with the silver nanoparticle, thereby providing high adhesion to the surface of the electrolytic copper conductor layer. Show. With the silver nanoparticles adhering to the surface of the electrolytic copper conductor layer as the core, the lamination of the silver nanoparticles from which the coating agent molecular layer has been removed proceeds. At that time, a part of the fusion of the laminated silver nanoparticles proceeds. In parallel, evaporation of the coating molecule dodecylamine, which is removed and dissolved in the dispersion solvent, and the dispersion solvent N14 proceed on the surface of the coating liquid layer.

(Step B-4) Third laser light irradiation step:
Finally, from the surface of the coating liquid layer, a laser beam having a wavelength of λ ₃ = 1064 nm is irradiated in a vertical direction (incident angle 0) with an irradiation spot diameter D ₃ = 100 μm and an average laser beam intensity P ₃ = 1,500 W / mm ^2. Irradiate from (°). Under this condition, by performing laser light irradiation for a total irradiation time t ′ ₃ = 3 seconds, alloying by mutual diffusion on the surface of the conductor layer of electrolytic copper, fusion of laminated silver nanoparticles, Low temperature sintering is completed. In parallel, on the surface of the coating liquid layer, the evaporation of the dispersion solvent N14 and the coating molecule molecule dodecylamine dissolved in the dispersion solvent is accelerated, and a thin film layer of a silver nanoparticle sintered body is formed. Is completed.

(Comparative Example 2)
In Comparative Example 2, the thickness of the coating liquid layer of the metal nanoparticle dispersion applied on the copper substrate is three times that of Example 2, and the laser light that reaches the surface of the conductor layer of electrolytic copper when irradiated with laser light. In this example, the metal nanoparticle sintered body film is formed by selecting a condition that makes the strength equal to that in Example 2.

  As the substrate, a substrate having an electrolytic copper conductor layer is employed, and a liquid repellent coating layer is coated on the entire surface of the electrolytic copper conductor layer. This liquid repellent coating layer is in a state where liquid repellent: fluorine-based surface treatment agent EGC-1720 is uniformly applied to a thickness of about 10 nm.

  As a metal nanoparticle dispersion liquid, a dispersion layer N14 (tetradecane) formed by forming a coating molecular layer of dodecylamine (melting point: 28.3 ° C., boiling point: 248 ° C.) on the surface of silver nanoparticles having an average particle diameter D of 3 nm. Viscosity of 2.0 to 2.3 mPa · s (20 ° C.), melting point of 5.86 ° C., boiling point of 253.57 ° C., manufactured by Nikko Petrochemical Co., Ltd.). The silver nanoparticle dispersion contains 20 parts by mass of the coating molecule dodecylamine and 52 parts by mass of the dispersion solvent N14 per 100 parts by mass of the silver nanoparticles. The liquid viscosity of the silver nanoparticle dispersion is 10 mPa · s (20 ° C.).

  The silver nanoparticle dispersion is applied to the surface of the electrolytic copper conductor layer coated with the liquid repellent coating layer with a coating liquid thickness of 9 μm to prepare a silver nanoparticle dispersion liquid coating layer.

  The coating liquid layer of this silver nanoparticle dispersion is subjected to a preliminary drying treatment at 100 ° C. for 60 seconds.

Laser light having a wavelength λ ₁ = 1064 nm is irradiated from the surface of the silver nanoparticle dispersion liquid coating layer from the vertical direction (incident angle 0 °) with an irradiation spot diameter D ₁ = 100 μm. At that time, the light transmittance of the coating solution layer of the silver nanoparticle dispersion decreases approximately in proportion to exp (−A · d) with respect to the thickness d of the coating solution layer. Therefore, the apparent transmittance of the silver nanoparticle dispersion coating liquid layer is reduced to T _1-upper = 40% under the condition of Comparative Example 2 while the value of Example 1 is T _1-upper = 74%. To do. Therefore, under the condition of the coating liquid thickness of 9 μm, the apparent reflectance R _1-upper = 3% on the surface of the silver nanoparticle dispersion liquid coating liquid layer, and the apparent transmittance T _{1− of the} silver nanoparticle dispersion liquid coating liquid layer _upper = 40%, apparent reflectance R _1−lower = 60% at the interface between the electrolytic copper conductor layer / silver nanoparticle dispersion coating solution layer.

The intensity of the laser beam applied to the interface between the electrolytic copper conductor layer / silver nanoparticle dispersion liquid coating solution layer is made substantially equal to the laser beam intensity in Example 2. Therefore, the average laser light intensity is irradiated to the surface of the coating liquid layer, with respect to the value P ₁ = 13,000W / mm ² of Example 2, under the conditions of this Comparative Example 2, P ₁ = 19,000W / It has greatly increased to mm ^2.

  The heating of the electrolytic copper conductor layer surface depends on the intensity of the laser beam applied to the interface between the electrolytic copper conductor layer / silver nanoparticle dispersion liquid coating solution layer. Under the above irradiation conditions, the intensity of the laser beam applied to the interface is substantially equal, so that the temperature of the surface of the conductive layer of electrolytic copper is also substantially equal. On the other hand, the heating of the coating liquid layer surface depends on the average laser light intensity irradiated on the surface of the coating liquid layer. Under the above irradiation conditions, the average laser light intensity irradiated on the surface of the coating liquid layer is increased by about 1.5 times, so that the temperature of the coating liquid layer surface is significantly increased.

As a result, at the time when the irradiation time t ₁ = 3 seconds passed (P ₁ · t ₁ ≧ 57,000 ms · W / mm ² ), at the interface between the electrolytic copper conductor layer / silver nanoparticle dispersion coating liquid layer The temperature reaches T _{1 -bottom} = 120 ° C., and the temperature of the surface of the silver nanoparticle dispersion liquid coating solution reaches T _1-top = 110 ° C.

The liquid repellent: EGC-1720 itself used for the liquid repellent coating layer for coating the surface of the electrolytic copper conductor layer does not absorb the laser beam having the wavelength λ ₁ = 1064 nm. On the other hand, at a temperature T _1-bottom = 120 ° C. at the interface between the electrolytic copper conductor layer / coating liquid layer, the liquid repellent: EGC-1720 dissolves in the dispersion solvent N14 of the silver nanoparticle dispersion. As a result, the liquid repellent coating layer that was present at the interface between the silver nanoparticle dispersion coating solution layer and the electrolytic copper conductor layer in the portion that was in contact with the silver nanoparticle dispersion coating solution layer and irradiated with the laser beam. Is selectively removed.

Subsequently, a laser beam having a wavelength λ ₂ = 1064 nm is irradiated from the surface of the silver nanoparticle dispersion coating liquid layer from the vertical direction (incident angle 0 °) with an irradiation spot diameter D ₂ = 100 μm. Even under this irradiation condition, the light transmittance of the coating solution layer of silver nanoparticle dispersion decreases approximately in proportion to exp (−A · d) with respect to the thickness d of the coating solution layer. Therefore, at the start of irradiation, the apparent transmittance of the silver nanoparticle dispersion liquid coating layer is the value of Example 2, T _2-upper = 74%, whereas in the condition of Comparative Example 2, T _2-upper = Reduce to 40%. Therefore, under the condition of the coating liquid thickness of 9 μm, the apparent reflectance R _2-upper = 3% on the surface of the silver nanoparticle dispersion liquid coating liquid layer, and the apparent transmittance T _{2− of the} silver nanoparticle dispersion liquid coating liquid layer. _upper = 40%, apparent reflectance R _2−lower = 60% at the interface between the electrolytic copper conductor layer / silver nanoparticle dispersion coating solution layer. Therefore, the apparent light absorption rate A _{2 -upper} = 57% in the silver nanoparticle dispersion coating liquid layer, the ratio of light penetrating into the electrolytic copper conductor layer (effective light absorption rate) A _2−lower = It is 16%.

The intensity of the laser beam applied to the interface between the electrolytic copper conductor layer / silver nanoparticle dispersion liquid coating solution layer is made substantially equal to the laser beam intensity in Example 2. Therefore, the average laser light intensity irradiated on the surface of the coating liquid layer is P ₂ = 3,000 W / mm 2 under the condition of Comparative Example 2 as compared with the value P ₂ = 1,500 W / mm ^{2 in} Example 2. It has greatly increased to mm ^2.

On the surface of silver nanoparticles having an average particle diameter of 3 nm, localized plasmon absorption occurs by irradiation with laser light having a wavelength λ ₂ = 1064 nm. At that time, the coating molecule dodecylamine covering the surface of the silver nanoparticle is excited by the localized plasmon and is in a vibrationally excited state. As a result, the release of the coating molecule dodecylamine covering the surface of the silver nanoparticles is promoted.

At that time, under the irradiation conditions of Comparative Example 1, when the irradiation time t ₂ = 1 second has elapsed (P ₂ · t ₂ ≧ 3,000 ms · W / mm ² ), the electrolytic copper conductor layer / silver nanoparticles The temperature at the interface of the dispersion coating liquid layer reaches T _2-bottom = 160 ° C, and the temperature of the surface of the silver nanoparticle dispersion coating liquid layer reaches T _2-top = 160 ° C.

Therefore, at the temperature T _{2 -bottom} = 160 ° C. at the interface between the electrolytic copper conductor layer / silver nanoparticle dispersion coating solution layer, the release of the coating molecule dodecylamine in the vibrationally excited state is promoted. The silver nanoparticles from which the coating layer has been removed adhere to the surface of the electrolytic copper conductor layer.

Further, at a temperature T _2-top = 160 ° C. on the surface of the coating solution layer, the _release of the coating molecule dodecylamine in a vibrationally excited state is promoted, resulting in the removal of the surface coating layer of the silver nanoparticles. The silver nanoparticles from which the surface coating layer has been removed are fused together to form an aggregate. That is, in the vicinity of the surface of the silver nanoparticle dispersion coating liquid layer, silver nanoparticles are fused to each other to form a layer forming an aggregate. Using the silver nanoparticle aggregate layer as a core, the silver nanoparticle aggregates produced in the silver nanoparticle dispersion liquid coating layer are connected at a sparse density.

At this time, the silver nanoparticle aggregate layer blocks laser light having a wavelength of λ ₂ = 1064 nm and inhibits the laser light from entering the silver nanoparticle dispersion coating liquid layer. As a result, the dissociation process of the coating molecule dodecylamine, which is promoted by the vibration excitation of the coating molecule dodecylamine, caused by the irradiation with the laser beam having the wavelength λ ₂ = 1064 nm, in the coating layer of the silver nanoparticle dispersion liquid is Be inhibited. That is, the silver nanoparticle dispersion liquid coating liquid layer is in a state where silver nanoparticles holding the coating agent molecule layer made of the coating agent molecule dodecylamine remain in a considerable ratio.

  On the other hand, on the surface of the coating liquid layer, the transpiration of the dispersion solvent N14 and the coating agent molecule dodecylamine dissolved in the dispersion solvent rapidly proceeds.

  As a result, when the dispersion solvent evaporates, a layer structure in which agglomerates of silver nanoparticles are connected at a sparse density is formed on the surface of the coating liquid layer, and a coating molecular layer is formed in the lower layer portion. There is a state in which there is a region where silver nanoparticles holding s are contained in a considerable ratio.

Finally, from the surface of the coating solution layer, a laser beam having a wavelength λ ₃ = 1064 nm is irradiated in a vertical direction (incident angle 0) with an irradiation spot diameter D ₃ = 100 μm and an average laser beam intensity P ₃ = 3,000 W / mm ^2. Irradiate from (°). In Comparative Example 2, under this irradiation condition, the apparent reflectance R _3-upper = 3% on the surface of the coating liquid layer at the start of irradiation, and the apparent transmittance of the coating liquid layer (aggregate layer of silver nanoparticles). T _{3 -upper} = 15%, Apparent reflectance R _{3 -metal-layer} = 95% at the interface of the silver nanoparticle laminate / coating liquid layer. Therefore, the apparent light absorption rate A _3-upper = 82% in the coating liquid layer (silver nanoparticle aggregate layer), that is, the ratio of light penetrating into the silver nanoparticle aggregate layer (effective light absorption) Rate) A _{3-metal-layer} = 82%.

  Under this condition, low-temperature sintering proceeds in the layer structure portion formed by the aggregation of silver nanoparticles connected on the surface of the coating solution layer at a sparse density. However, the lower layer portion is a region where silver nanoparticles holding the coating agent molecular layer are contained in a considerable ratio, and low temperature sintering does not proceed in the lower layer portion. Of course, the adhesion of the electrolytic copper to the surface of the conductor layer is poor.

  The method for forming a highly adhesive metal nanoparticle sintered body film of the present invention includes a fine wiring board for SIP (System in Package) (interposer) or a fine wiring board for SIB (System in Board). Substrate) can be applied.

It is a figure which shows typically the process of forming a metal nanoparticle sintered compact film | membrane on the board | substrate which coat | covered the surface with the liquid repellent coating layer. Utilizing the step of performing low-temperature sintering by laser light irradiation under the condition that the coating liquid thickness of the metal nanoparticle dispersion (silver nanoparticle dispersion) applied to the surface of the metal substrate (Cu substrate) is thin, It is a figure which shows typically the process which forms a metal nanoparticle (silver nanoparticle) sintered compact film | membrane. When performing low-temperature sintering by laser light irradiation under the condition that the coating thickness of the metal nanoparticle dispersion (silver nanoparticle dispersion) applied to the surface of the metal substrate (Cu substrate) is thin, the coating liquid layer It is a figure which shows typically the mechanism in which an unsintered silver nanoparticle remains in the lower area | region of.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Substrate 2 Liquid repellent coating layer 5 Metal nanoparticle dispersion coating liquid layer 6 Metal nanoparticle sintered body film

Claims (9)

A method of forming a highly adhesive metal nanoparticle sintered body film on a substrate,
Step 1 to Step 4 below:
(Process 1)
Applying a metal nanoparticle dispersion liquid in a predetermined planar shape on a substrate coated with a liquid repellent coating layer to produce a coating liquid layer;
(Process 2)
Irradiating a laser beam having a wavelength λ ₁ from the surface of the coating liquid layer with an average laser beam intensity P ₁ from a vertical direction (incident angle 0 °);
(Process 3)
After the step 2, a step of irradiating the surface of the coating liquid layer with a laser beam having a wavelength λ ₂ from the vertical direction (incident angle 0 °) with an average laser beam intensity P ₂ ;
(Process 4)
After the step 3, the step of irradiating a laser beam having a wavelength λ ₃ from the surface of the coating solution layer with an average laser beam intensity P ₃ from the vertical direction (incident angle 0 °),
The metal nanoparticle dispersion is
An average particle diameter is selected in the range of 1 to 100 nm, a metal nanoparticle dispersion liquid in which metal nanoparticles are dispersed in a dispersion solvent,
The metal nanoparticles contained in the dispersion can be coordinately bonded to metal atoms on the surface of the metal nanoparticles using lone electron pairs on nitrogen, oxygen, and sulfur atoms. The surface of the metal nanoparticles is coated with an organic compound having a boiling point of 150 ° C. or higher as a coating agent molecule,
The dispersion solvent is a nonpolar organic solvent having a boiling point of 150 ° C. or higher or a low polarity organic solvent,
In the dispersion, when the volume ratio of the metal nanoparticles contained is V _particle volume%, the thickness d of the coating solution layer satisfies 0.5 μm ≧ d · (V _particle / 100). Is selected;
Laser light having a wavelength lambda ₁ is not substantially absorbed into the metal nanoparticles have a wavelength lambda ₁ to be absorbed in the material constituting the surface of said substrate,
When adopting a substrate made of insulating resin material,
Mean laser beam intensity P ₁ is selected in the range of ^{50W / mm 2 ~800W / mm 2} ,
When adopting a substrate made of metal material,
The average laser light intensity P ₁ is selected in the range of 5,000 W / mm ^{2 to} 15,000 W / mm ² ;
Laser light having a wavelength lambda ₂ has a wavelength lambda ₂ to be absorbed by the metallic nanoparticles,
When adopting a substrate made of insulating resin material,
Mean laser beam intensity P ₂ is selected within the range of ^{5W / mm 2 ~200W / mm 2} ,
When adopting a substrate made of metal material,
Mean laser beam intensity P ₂ is selected within the range of ^{500W / mm 2 ~3,000W / mm 2} ;
Laser light having a wavelength lambda ₃ has a wavelength lambda ₃ that is absorbed by the metal constituting the metal nanoparticles,
When adopting a substrate made of insulating resin material,
Mean laser beam intensity P ₃ is selected in the range of ^{5W / mm 2 ~200W / mm 2} ,
When adopting a substrate made of metal material,
Mean laser beam intensity P ₃ is, 500W / mm ² ~3,000W / mm high adhesion method for forming the metal nanoparticle sintered body film, which is selected ² range. The substrate is a substrate coated with a polyimide layer;
The method for forming a highly adhesive metal nanoparticle sintered body film according to claim 1, wherein the material constituting the surface of the substrate is the polyimide layer. The substrate is a substrate having a conductor layer made of metallic copper or a copper alloy having a copper content of 97% by mass or more,
The method for forming a highly adhesive metal nanoparticle sintered body film according to claim 1, wherein the material constituting the surface of the substrate is a conductor layer composed of the metallic copper. The metal nanoparticles are silver nanoparticles,
Laser light having a wavelength lambda ₁ is a Nd / YAG laser beam having a wavelength lambda ₁ = 1064 nm,
Mean laser beam intensity P ₁ is selected in the range of ^{50W / mm 2 ~800W / mm 2} ;
Laser light having a wavelength lambda ₂ is a harmonic of the Nd / YAG laser beam having a wavelength lambda ₂ = 1064 nm of Nd / YAG laser light or the wavelength lambda ₂ = 532 nm,,
Mean laser beam intensity P ₂ is selected within the range of ^{5W / mm 2 ~200W / mm 2} ;
Laser light having a wavelength lambda ₃ is a Nd / YAG laser beam having a wavelength lambda ₃ = 1064 nm,
Mean laser beam intensity P ₃ is, 5W / mm ² ~200W / method of forming a highly adhesive metal nanoparticle sintered body film according to claim 2, characterized in that it is selected in the range of mm ^2. The metal nanoparticles are silver nanoparticles,
Laser light having a wavelength lambda ₁ is a Nd / YAG laser beam having a wavelength lambda ₁ = 1064 nm,
The average laser light intensity P ₁ is selected in the range of 5,000 W / mm ^{2 to} 15,000 W / mm ² ;
Laser light having a wavelength lambda ₂ is a Nd / YAG laser beam having a wavelength lambda ₂ = 1064 nm,
Mean laser beam intensity P ₂ is selected within the range of ^{500W / mm 2 ~3,000W / mm 2} ;
Laser light having a wavelength lambda ₃ is a harmonic of the Nd / YAG laser beam having a wavelength lambda ₃ = 1064 nm of Nd / YAG laser light or the wavelength lambda ₃ = 532 nm,,
Mean laser beam intensity P ₃ is, 500W / mm ² ~3,000W / method of forming a highly adhesive metal nanoparticle sintered body film according to claim 3, characterized in that it is selected in the range of mm ^2. Irradiation spot diameter D ₁ of the laser beam of wavelength lambda ₁ is selected in a range of 10 m to 500 m;
Irradiation spot diameter D ₂ of the laser beam having a wavelength lambda ₂ is selected in the range of 10 m to 500 m;
Irradiation spot diameter D ₃ of the laser beam having a wavelength lambda ₃ is highly adhesive metal nanoparticle sintered body according to any one of claims 2-5, characterized in that it is selected in the range of 10μm~500μm Method for forming a film. Irradiation spot diameter D ₁ of the laser beam having a wavelength lambda _1, the irradiation spot diameter D ₂ of the laser beam having a wavelength lambda _2, the irradiation spot diameter D ₃ of the laser beam having a wavelength lambda ₃ are selected D ₁ = D ₂ = D ₃ The method for forming a highly adhesive metal nanoparticle sintered body film according to claim 6, wherein: The method for forming a highly adhesive metal nanoparticle sintered body film according to any one of claims 2 to 7, wherein an alkylamine having a boiling point of 150 ° C or higher is selected as the coating agent molecule. After the step of preparing the coating liquid layer in (Step 1), prior to (Step 2),
The method for forming a highly adherent metal nanoparticle sintered body film according to any one of claims 1 to 8, further comprising a predrying treatment step for predrying the coating liquid layer.

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